Cairo - Egyptian military units deployed in the streets of Cairo on Friday, and protesters targeted offices of the ruling party, as massive crowds of anti-government demonstrators defied an overnight curfew and appeared to grow more violent.

The deployment of troops and armored fighting vehicles came after heavily armed riot police battled thousands of protesters across Egypt on Friday in an effort to squelch a burgeoning pro-democracy movement that appeared to be gaining strength.

Crowds surged onto the streets of Cairo and other cities immediately after noon prayers, responding to a call for protests dubbed "Angry Friday." Toward sunset, the demonstrations seemed to grow larger, even as police fired guns, tear gas and water cannons.

The Egyptian government imposed an overnight curfew on Cairo, Alexandria and Suez starting at 6 p.m. (11 a.m. EST) and ending at 7 a.m., but the surging crowds did not heed it, appearing only to become more violent and intense.

State television said the military would work with police to enforce a ban on demonstrations, and military units were seen deploying on the streets of this capital of about 18 million people. CNN showed one military armored fighting vehicle blocking a street with its gun turret pointing down the road. It was soon surrounded by a chanting crowd.

With President Hosni Mubarak preparing to appear on television to address the nation for the first time since the crisis began, riot police seemed to be pulling back from their positions.

Protesters, meanwhile, pressed forward and grew less organized and more violent than they had been in daylight. Demonstrators torched armored personnel carriers on some Cairo streets, and live video reports showed police security trucks careening wildly through the crowds. Gunshots and the firing of tear gas continued uninterrupted. It was not immediately clear whether the police were firing live ammunition or rubber bullets.

There were reports that Mubarak was sending the military out to patrol the streets alongside or instead of the heavily armed riot police. As the army's tan camouflage vehicles took the place of the black police vehicles in some areas, the crowds surrounded them, cheering and chanting and appearing to be urging the soldiers to join their cause.

Crowds attempted to gather at the Cairo headquarters of Mubarak's ruling National Democratic Party, and fires were set, although it was not immediately clear what was burning. In the cities of Mansoura, north of Cairo, and Suez, east of the capital, party headquarters were ransacked by protesters, the Associated Press reported.

In Washington, White House press secretary Robert Gibbs called on the Egyptian government to respect the rights of protesters and to restore Internet and social networking services.

Earlier, on the 6th of October Bridge, which spans the Nile in the heart of this teeming capital, two protesters were shot by police and collapsed on the ground, unresponsive. They were loaded into a van that appeared headed for a nearby hospital.

But police stopped the van, pulled out the people accompanying those who had been shot and began beating them with wooden batons. The fate of those who were shot was not known.

Protesters clashed with police in Suez and Alexandria as well. In Suez, a port city that has been the site of some of the most intense confrontations this week, thousands of protesters overwhelmed riot police after a two-hour battle at a police station.

The protesters hurled what appeared to be gasoline bombs at armored personnel carriers, setting at least a half dozen of the vehicles on fire with the occupants inside. The protesters then freed the prisoners who were being held at the station. They began looting, carting off anything they could find in the police building, including weapons. Police fled.

Like previous demonstrations this week, Friday's rallies appeared to be primarily made up of secular, middle-class citizens demanding the end of the decades-long rule of Egyptian President Hosni Mubarak. A government shutdown of Internet connections and cellphone service, intended to disrupt communication among the demonstrators, appeared to have little impact.

"This is no longer a time of fear. It's a time of change," said Mohammed Nabil, a 35-year-old doctor participating in his first protest. "We want Mubarak to leave and end 30 years of oppression."

Mohamed ElBaradei, a political reform advocate and Nobel Peace Prize laureate who returned to Egypt from abroad to participate, was arrested Friday and placed under house arrest, the Associated Press reported.

ElBaradei, the former chief of the Vienna-based International Atomic Energy Agency, has said he wants to lead Egypt in a peaceful transition to democratic government. He could challenge Mubarak in the presidential election in September.

Across Cairo, as the sun set, clouds of tear gas hovered near virtually every minaret on the skyline, marking the spots where the demonstrations began. A roar of chanting and cheering rose from the crowds on the streets, accompanied by the near-constant wail of sirens and the staccato beat of gunfire and exploding tear gas canisters.

On the 6th of October bridge - so named to commemorate the 1973 Arab invasion of Israel that launched the Yom Kippur War - and on other spans over the Nile, protesters repeatedly surged forward from one end, only to be driven back by police surging from the other. The demonstrators were trying to converge on the centrally located Tahrir Square, where about 15,000 demonstrators protested Tuesday. But police continued to blockade it.

Live video showed seas of people swarming against row after row of helmeted police, who struck the protesters repeatedly with wooden batons. Clouds of tear gas and deluges from water cannons dispersed the masses momentarily. But the protesters soon converged again, chanting slogans

Protesters called for the U.S. government to support their cause. Osama el-Ghazi Harb, a prominent Egyptian writer, held aloft an empty tear gas cannister that only minutes earlier had been fired at him and several hundred other protesters.

"I'm very sorry to say that it was made in the U.S.A.," Harb said. "The U.S. must condemn this use of force and, at the proper moment, tell Mubarak to get out."

The crowds shouted "Down, down, Hosni Mubarak" and stamped on posters of the president. Protesters waved Egyptian flags and occasionally thew stones, but for the most part remained peaceful.

The Muslim Brotherhood, Egypt's largest opposition group, had largely been absent from the protests that have roiled the nation this week. But the group said it would fully participate in Friday's demonstrations, potentially drawing many more people to the streets.

The showdown Friday could be a crucial test of Mubarak's staying power. Egypt's Internet and cellphone shutdown appeared to be the most drastic move against anti-government activists' use of technology since the Iranian government cracked down on protests in 2009. Overnight, security services raided the homes of opposition leaders - including those of the Muslim Brotherhood - and arrested dozens.

Neither Mubarak, who has ruled here for 30 years, nor his son, Gamal, a possible successor, has appeared in public since the demonstrations began Tuesday.

But Safwat el-Sharif, secretary general of Mubarak's ruling National Democratic Party, expressed sympathy for protesters' concerns Thursday and said the party was "ready for a dialogue" with youth activists, whom he applauded for expressing their views and described as "Egypt's future."

Nevertheless, Sharif discouraged demonstrators from gathering Friday. Egypt's Interior Ministry has banned all demonstrations and arrested hundreds, defying a call by the United States to allow peaceful protests.

"The minority does not force its will on the majority," Sharif told journalists as he spoke beneath a large photograph of Mubarak at his party's headquarters in Cairo a short walk from Tahrir Square.

Egypt's protesters have said they were inspired by Tunisia, where demonstrators ousted the country's president this month. But Sharif said Egypt would not "imitate" other countries.

This week's demonstrations have fed uncertainty about Mubarak's political future and Egyptian stability and wreaked havoc on the local stock market, which was halted for a half-hour on Thursday amid a steep slide in shares.

U.N. Secretary General Ban Ki-moon appealed on Friday for Egypt's leaders and its people not to let violence escalate.

"All concerned, people or leaders, should ensure that the situation in that region, particularly in Egypt should not lead to further violence," Ban said at the World Economic Forum meeting in Davos, Switzerland.