Nearly 100,000 Yemenis protested Friday in a main square of the capital, demanding the president's ouster in the biggest rally since Ali Abdullah Saleh left for Saudi Arabia after he was wounded in an attack on his palace.

U.S. officials told NBC News on Friday that the attack on Saleh last week was an "inside job" or assassination attempt using an explosive device and not a rocket attack as earlier reported. The officials said, however, there was "no evidence" an attempted coup."

Saleh was wounded in a blast that hit a mosque where he was praying in his presidential palace on June 3. Badly burned, Saleh was rushed to Saudi Arabia for treatment along with a number of top officials from his regime who also were wounded in the blast.

Officials told NBC News they based their conclusion in part on the serious wounds Saleh suffered, severe facial burns and large shard of wood that went through his chest and punctured his lung. There is speculation the wood came from a lecturn, NBC News reported.

Saleh's evacuation for medical treatment has thrown Yemen into a dangerous political standoff, with opponents insisting he now be pushed completely out of power and his allies seeking to preserve his rule.

But the president's allies say he could return within days and have been resisting U.S. and Saudi pressure to start now on a handover of power. Saleh, who has ruled for nearly 33 years, has held out against a wave of daily protests since late January demanding his removal, throwing the country into turmoil. Before he was wounded, opposition tribesmen rose up and battled for two weeks with government forces in fighting that shook the capital.

The United States fears that the impoverished country's power vacuum will give even freer rein to al-Qaida's branch in Yemen, which Washington believes is the terror network's most active franchise. Already, Islamic militants - some suspected of ties to al-Qaida - have taken control of at least two areas in the restive south, a provincial capital Zinjibar and a nearby town Jaar.

On Friday morning, warplanes hit militant positions north of Jaar, witnesses and security officials said. They said there were casualties but the number was not known. The night before, troops shelled other militant positions near the town with artillery, killing at least six militants, according to medical officials. The medical and security officials spoke on condition of anonymity because they were not authorized to talk to the press.

In Sanaa's Taghyeer, or "Change," Square on Friday, the crowds of protesters demanded that the vice president - who is acting leader in Saleh's absence - allow the creation of a new government. "The people want a transitional government," they chanted.

Opposition tribesmen marched through the square with the bodies of 41 of their fighters they say were killed a week ago when troops bombarded the Sanaa home of one of their leaders. The tribe's chief, Sheik Sadeq al-Ahmar, led a march of around 10,000 people from the square to a cemetery in the capital, as protesters chanted, "The people want the butcher put on trial," referring to Saleh.

In another part of the city, about three miles away, several thousand Saleh supporters held a rally outside his presidential palace. No friction between the two sides was reported.

Similar anti-Saleh protests were held in cities around the country, including in Taiz, Yemen's second largest city, where tribesmen have moved in to protect protesters who came under attack last week in a fierce crackdown by government troops. In recent days, government forces and tribesmen have been fighting in the city, trading gunfire and shelling.

Since Saleh's evacuation, Sanaa has been under a fragile cease-fire, with government troops still deployed in the streets where they once battled al-Ahmar's tribal fighters. The situation has raised fears of a new explosion of violence if a political solution is not found soon - or if the president does indeed return.

The United States and Saudi Arabia are pressing Saleh's ruling party to move ahead with a Gulf Arab-mediated agreement under which he would formally leave power in exchange for immunity, a new unity government would be formed between the ruling party and opposition parties and new elections would be held within two months.

But youth activists leading the street protests reject the deal, saying it would allow elements of Saleh's regime to remain in power. They demand the creation of a transitional government made up of technocrats.

In Abu Dhabi, U.S. Secretary of State Hillary Rodham Clinton on Thursday called on all sides to honor a cease-fire. She said Washington was pushing for an "immediate, orderly and peaceful transition" in Yemen.

The upheaval of the past months has left Saleh too preoccupied to focus on the fight against al-Qaida, and the United States has stepped up its covert operations in Yemen. American officials said Thursday that a U.S. airstrike on June 3 killed a midlevel al-Qaida operative named Abu Ali al-Harithia in southern Yemen.

Emboldened, the militants have made inroads deep in the Yemeni hinterland and on its rugged mountain ranges.

In Abyan, residents said suspected al-Qaida militants were openly training in camps and using live ammunition for target practice. They were also carrying out identity checks on travelers on roads leading to neighboring provinces.

Residents of the southern province of Shabwa said suspected al-Qaida militants and sympathizers had set up checkpoints on the road to the nearby province of Hadramawt. They also controlled the towns of Rawdah and Houtah, where they freely roamed the streets.

There is a blurred line between Yemen's large and diverse community of militants and al-Qaida, which is thought to have no more than 300 hard-core members in Yemen. The militants have varying levels of links to the terror network.

Saleh has allied with many of these groups to promote his own interests against political rivals that include moderate Islamists, leftist parties and secular-minded intellectuals. He has sought the militants' help to "Islamize" the south, where secular traditions endure two decades after it was united with the conservative north.

Source: The Associated Press