The Kabul pictures were taken as American vehicles fled the scene of an accident in which several Afghans were killed and injured after a US Army truck lost control and hit a number of civilian vehicles. Shot from a hillside above where the original accident took place, they show a crowd of Afghans throwing stones at the American vehicles.

A sequence of pictures show US vehicles leaving at high speed as the crowd stones them. In one sequence, a clearly unarmed Afghan man is seen with an American Humvee in the background, then as part of a group of men throwing stones towards the Americans. Two frames later his lifeless body is on the ground, having apparently been shot in the chest.

Another picture shows the body of an 18-year-old mechanic named Maiwan. His family said he was also hit by bullets fired from a US Humvee towards the crowd. His brother Jawad, 19, said Maiwan died from wounds to his knee and chest. "We are not the sort of people to do anything against US forces," said Jawad. "Maiwan was quiet and friendly. My father loved him too much, more than the rest of us."

The photographer, Atif Ahmadzai, 34, said: "I thought at first they were firing into the air. I was on the hill taking the pictures and, as they fired towards me, I ducked. One bullet grazed my thigh. Two people were killed behind me." He said he saw six bodies in total.

The day after the rioting he took the pictures to the US embassy. "I told them,'Just look at the people in the pictures, they are all unarmed'," he said. A statement released by the US military said a US Army truck had suffered a brake failure, causing it to lose control and hit up to 13 Afghan civilian vehicles, killing one person. The statement said: "There are indications that at least one coalition military vehicle fired warning shots over the crowd." US forces have launched an investigation into the incident, the results of which are due to be published next week.

All the witnesses to the incident reported at least one US vehicle opened fire on the civilians. "I saw with my own eyes that the soldier fired on the people," said Nazir Akhmad, 32, who owns a petrol station near where the accident occurred. "Her gun was pointed in the air but then she brought it down and started firing. The first bullet killed a boy called Khaled."

The US military declined to comment yesterday on its investigation. The US spokesman, Col Tom Collins, said: "I can't comment on the results of the investigation but there is no doubt that our soldiers thought there was fire emanating from the crowd."

The US military said the raid, which also involved Iraqi forces, had targeted "individuals involved in punishment and torture cell activities" and was part of an effort to stem the sectarian violence in Baghdad and avert a broader civil war.

The military said three people had been arrested but made no mention of fatalities. Residents reported a fierce firefight that lasted more than two hours.

"This operation used weapons that are unreasonable to detain someone, like using planes," Mr Maliki said. He apologised for the operation and vowed: "This won't happen again." He also sent an envoy to Sadr City to offer cash payments to families of the dead and wounded.

At the end of June, Mr Maliki unveiled a blueprint for national reconciliation. But neither that, nor a succession of security offensives, have halted the bloodshed in the capital. Four roadside bombs in Baghdad yesterday killed at least 19 people. The deadliest blast killed at least 10 and wounded 69 others in a central Baghdad market. Other bombs targeted police and a busy bus station. Two Iraqi journalists were reportedly killed in separate incidents in Baghdad.

The impoverished Sadr City district provides many of the footsoldiers for Mr Sadr's Mahdi army militia, which is widely suspected of conducting sectarian attacks against Sunnis.

Mr Maliki has vowed to restore security to the capital and rein in the militias but his task is complicated by the knowledge that some groups are linked to some of his main political allies. For example, since the Mahdi army staged two failed uprisings against coalition troops in 2004, supporters of the anti-western cleric have entered politics, forming a powerful bloc within Mr Maliki's ruling Shia alliance.

In an attempt to break up the death squads in Baghdad, US and Iraqi forces have staged a number of raids in Sadr City, but commanders have been at pains to point out the crackdown is not aimed at particular groups. With anger among Iraqi Shias already riding high owing to the Lebanon crisis Mr Maliki knows he can ill afford to further alienate Sadr supporters.

Abdul Jabbar, a political science professor at Baghdad University, said: "The prime minister is in a tricky position. He is under pressures from the Sadrists in his own alliance and at the same time from the Americans."

Four U.S. service members were injured when the UH60 Blackhawk helicopter crashed Tuesday with six people on board during a routine flight to survey the area, the U.S. command said in a statement Wednesday. The four injured troops were in stable condition, and it did not appear the crash was due to hostile fire, the U.S. said.

The ongoing violence in Baghdad has prompted U.S. commanders to reinforce troop strength in the city. Over the past weeks, a force expected to number nearly 12,000 has been assembling here to try to take the streets back from Sunni and Shiite extremists.

A U.S. statement Tuesday said about 6,000 additional Iraqi troops were being sent to the Baghdad area, along with 3,500 soldiers of 172nd Stryker Brigade Combat Team and 2,000 troops from the U.S. 1st Armored Division, which has served as a reserve force since November.

"We must dramatically reduce the level of violence in Baghdad that is fueling sectarianism," said Maj. Gen. J.D. Thurman, commander of the coalition forces in Baghdad, where strife between Shiites and Sunnis runs the highest.

"Iraqi and U.S. forces will help the citizens of Baghdad by reducing the violence that has plagued this city since the Samarra bombing," Thurman said. "Iraqi and Multinational Division-Baghdad soldiers will not fail the Iraqi people."

Much of the violence has been blamed on sectarian militias that have stepped up a campaign of tit-for-tat killings since the Feb. 22 bombing of a Shiite shrine in the northern city of Samarra.

Some of the reinforcements have already been seen patrolling a mostly Sunni neighborhood in western Baghdad, scene of armed confrontations between Sunni and Shiite gunmen.

Many of the militias responsible for sectarian violence are linked to political parties that are part of Prime Minister Nouri al-Maliki's national unity government, and they are reluctant to disband their armed wings unless others do the same.

The U.S. ambassador to Iraq, Zalmay Khalilzad, said there were talks under way between various Sunni and Shiite groups to reach agreements and sign pledges to end sectarian fighting.

Also Wednesday, Romanian President Traian Basescu arrived in Baghdad to meet Iraqi and U.S. officials and visit some of the country's 890 troops stationed there. Basescu was received by President Jalal Talabani and will meet other key U.S. and Iraqi officials.

In June, Romanian Prime Minister Calin Popescu Tariceanu proposed withdrawing Romania's troops from Iraq, but Basescu and the country's top security body said the next day they would remain.

In Basra, the city council said it has decided not to cooperate with a committee sent by the prime minister to supervise an emergency plan for the city, according to councilman Aqil Talib. He said the council wanted to meet first with al-Maliki to determine the committee's role.

The decision shows the tension between the central government and the religious Shiite political leadership in Basra.

In other violence Wednesday, gunmen on two motorcycles assassinated Col. Qassim Abdel-Qadir, administrative head of an Iraqi army division in the southern city of Basra, said a police official who did not want to be named for security reasons.

A roadside bomb exploded near a U.S. patrol in eastern Baghdad's Shiite neighborhood of Habibiya, killing one bystander and injuring one U.S. soldier, said police Lt. Bilal Ali.

Police also found the bodies of three men who were shot in the head and dumped in two locations in southwestern Baghdad, said police Lt. Maitham Abdul-Razzaq said.

A policeman was killed and another wounded when they were trying to defuse a roadside bomb late Tuesday in Samarra, 60 miles north of Baghdad, police Capt. Laith Mohammed said.

In New Zealand, the Foreign Ministry said a Cook Islands national working as a driver in Iraq was killed in a bomb attack late Tuesday.

"This hanging is totally against Islam," Akhunzada said. "They use the name of Islam to go against Islam."

The Taliban have stepped up attacks in southern Afghanistan this year. More than 900 people have died in violence since May, mostly militants killed in fighting with security forces.

The violence, the deadliest since the Taliban regime's ouster in late 2001, has underscored the weak grip of the government of U.S.-backed President Hamid Karzai, particularly in the volatile south and east of the country.

Also in Musa Qala, British troops in a NATO-led security force accidentally shot and killed an armed Afghan policeman wearing civilian clothes after mistaking him for an insurgent outside a base on Tuesday, the British Ministry of Defense said.

Meanwhile, in the northwest of Afghanistan, some 400 militants were involved in clashes Monday in the Pashtun Kot district of Faryab province between forces loyal to rival ethnic Uzbek warlords Abdul Rashid Dostum and Abdul Malik, said Gen. Taj Mohammad, the Afghan National Army corps commander in northern Afghanistan.

Dostum is the current chief of staff of the Afghan Army's High Command.

At least one civilian was among the four people killed, and hundreds of others fled the fighting, Mohammad said.

The army and police sent hundreds of troops to restore calm and detained Khalem Salem, a Malik supporter who was involved in the fighting, Mohammad said.

It was not immediately clear what sparked the clashes, but the two groups had clashed 10 days earlier over a political dispute, leaving four dead.

Richards urged Canadians to continue their contribution to the international forces that have been trying to help stabilize the country since a Taliban government was ousted in 2001.

The NATO commander said the Canadians who have died in Afghanistan have "died for as good a cause as I can think of."

"If ever there was a just war, this is it," Richards said.

Must improve life 'soon,' general warns

He estimated it would take three to five years to significantly improve the lives of Afghans, but noted that ordinary Afghans are already grumbling about a lack of security.

"If it doesn't visibly improve soon, people are going to say we'd rather have the certain security - albeit the rotten life that goes with it - of the Taliban than go on fighting forever," Richards said.

"Can they stick with us a bit longer as we give them the confidence or do they really want to go back to the Taliban?"

The Taliban is particularly active in southern Afghanistan, where last week four Canadian soldiers were killed in fighting and one died in an accident.

The body of the most recent casualty - Master Cpl. Raymond Arndt, 32, of Peers, Alta. - arrived in a military transport at Trenton, Ont., on Monday evening. Arndt was killed in a traffic accident near Kandahar airfield on Aug. 5.

Afghan fighters thanked for defeating Soviets

Richards said the West should be grateful to Afghanistan because its militants, predecessors of the Taliban who are now attacking NATO troops, helped bring down the former Soviet regime.

The Soviet Union sent soldiers to Afghanistan in 1979 to keep the country in the Soviet orbit. But the Soviets couldn't quell the mujahedeen fighters and they withdrew in 1989.

The stress caused by a decade of bitter fighting and thousands of casualties contributed to the collapse of the Soviet government in 1991, Richards said.

"The people of this country actually fought and led to the collapse of the Soviet Union, emancipating millions and millions of people throughout the old Soviet bloc," Richards said on a visit to the large NATO base at Kandahar airfield.

The fighters, including al-Qaeda leader Osama bin Laden, were initially backed by the U.S. government, but it withdrew its support after the Russians retreated.

Al-Qaeda could have targeted Ottawa, Richards warns

The Taliban then came to power, holding on until American-led forces displaced it in 2001 after the Sept. 11 attacks in the United States.

"We can't risk the Taliban coming back in with Osama bin Laden," Richards said.

Al-Qaeda targeted Washington and New York, but "it could have been Ottawa. It could have been Toronto," Richards said.

"It wasn't something I did on the spur of the moment," said Magaoay, a native of Maui, Hawaii. "It took me a long time to realize what was going on. The war is illegal."

Magaoay said his disillusionment with the military began in boot camp in Twentynine Palms, Calif., where a superior officer joked about killing and mistreating Iraqis. When his unit was deployed to Iraq in March, Magaoay and his wife drove to Canada, joining a small group of deserters who are trying to win permission from the Canadian government to stay.

"We're like a tight-knit family," Magaoay said.

The Pentagon says deserters like Magaoay represent a tiny fraction of the nation's fighting forces.

"The vast majority of soldiers who desert do so for personal, family or financial problems, not for political or conscientious objector purposes," said Lt. Col. Bryan Hilferty, a spokesman for the Army.

Since 2000, about 40,000 troops from all branches of the military have deserted, the Pentagon says. More than half served in the Army. But the Army says numbers have decreased each year since the United States began its war on terror in Afghanistan.

Those who help war resisters say desertion is more prevalent than the military has admitted.

"They lied in Vietnam with the amount of opposition to the war and they're lying now," said Eric Seitz, an attorney who represents Army Lt. Ehren Watada, the first commissioned officer to refuse deployment to the war in Iraq.

Watada is under military custody in Fort Lewis, Wash., because he refused to join his Stryker brigade when it was sent to Iraq last month.

Watada said he doesn't object to war but considers the conflict in Iraq illegal. The Army has turned down his request to resign and plans to file charges against him.

Critics of the Iraq war have demonstrated on the lieutenant's behalf. Conservative bloggers call him a traitor and opportunist.

Joe Davis, spokesman for the Veterans of Foreign Wars, said deserters aren't traitors because they've done nothing to help America's enemies. But he rejects arguments that deserters have a moral right to refuse to fight wars they consider unjust.

"None of us can choose our wars. They're always a political decision," Davis said. "They're letting their buddies down and hurting morale - and morale is everything on the battlefront."

Because today's military is an all-volunteer force, troops seeking objector status must convince superior officers they've had an honest change of heart about the morality of war.

The last time the U.S. military executed a deserter was World War II. But hundreds face court-martials and imprisonment every year.

Members of the armed forces are considered absent without leave when they are unaccounted for. They become deserters after they've been AWOL for 30 days.

A 2002 Army report says desertion is fairly constant but tends to worsen during wartime, when there's an increased need for troops and enlistment standards are more lax. They also say deserters tend to be less educated and more likely to have engaged in delinquent behavior than other troops.

Army spokesman Hilferty said the Army doesn't try to find deserters. Instead, their names are given to civilian law enforcement officers who often nab them during routine traffic stops and turn them over to the military.

Commanders then decide whether to rehabilitate or court-martial the alleged deserter. There's an incentive to rehabilitate because it costs the military an average of $38,000 to recruit and train a replacement.

Jeffry House, an attorney in Toronto who represents Magaoay and other deserters, said there are about 200 deserters living in Canada. They have decided not to seek refugee status but instead are leading clandestine lives, he said.

Like many of the people helping today's war resisters, House fled to Canada to avoid the Vietnam War. About 50,000 Americans sought legal residency in Canada during the Vietnam era.

"You would apply at the border and if you didn't have a criminal record, you were in," House said.

He said changes in Canadian law make it harder for resisters to flee north. Now, potential immigrants must apply for Canadian residency in their home countries. Resisters say that exposes them to U.S. prosecution.