Forces loyal to Moammar Gadhafi fired tear gas at protesters who marched in Tripoli on Friday, calling for the Libyan leader's ouster in defiance of a fierce crackdown by regime supporters that has spread fear in the capital.

More than 1,500 protesters marched out of the Murad Agha mosque after noon prayers in the eastern Tripoli district of Tajoura, chanting "the people want to bring the regime down" and waved the red, black and green flag of Libya's pre-Gadhafi monarchy, adopted as the banner up the uprising.

The protesters transformed a nearby square, tearing down posters of the Libyan leader and replacing them with the flags. They spray-painted walls with graffiti reading, "Down with Gadhafi" and "Tajoura will dig your grave."

But soon after the march began, security forces fired tear gas at the crowd, according to an Associated Press reporter at the scene. The protesters scattered, but rejoined to continue their march. Then security forces fired live ammunition, scattering the protesters again _ though it was not immediately clear if they fired in the air or at people.

Similar protests a week ago were met by a brutal crackdown, when militiamen opened fire on demonstrators moments after they began their marches, killing a still unknown number. Since then, pro-Gadhafi forces have carried out a wave of arrests against suspected demonstrators, snatching some from their homes in nighttime raids.

"I am not afraid," said one 29-year-old man among the protesters. He said in the protests a week ago one of his relatives was shot to death _ not by militias, he said, but by a pro-Gadhafi infiltrator among the demonstrations. "There are many spies among us. But we want to show the world that we are not afraid" he said, speaking on condition of anonymity because of fears of retaliation.

Control of the capital is crucial to the Libyan leader, since it remains his strongest remaining bastion amid the uprising that began on Feb. 15 and has broken the entire eastern half of Libya out of his control. Even some cities in the west near Tripoli have fallen to the uprising, and the opposition has repelled repeated attacks by pro-Gadhafi forces trying to take back the territories.

A large force from a brigade led by one of Gadhafi's sons led a new attack Friday on Zawiya, the closest opposition-held city to Tripoli, a resident said. The troops from the Khamis Brigade _ named after the son _ attacked Zawiya's western side, firing mortars and then engaging in battles of heavy machine guns and automatic weapons with armed residents and allied army units, said the resident.

"Our men are fighting back the force, which is big," the resident said. Zawiya, about 30 miles (50 kilometers) west of Tripoli, has beaten back several assaults the past week.

Throughout the night and into the early hours Friday, pro-Gadhafi forces also fired mortars and anti-aircraft guns at the outskirts of opposition-held Misrata, Libya's third largest city located just east of Tripoli, a doctor in the city said. He said it appeared to be an intimidation tactic, causing no casualties.

The crisis has turned into something of deadlock between the two sides. Gadhafi's forces have been unable to take back significant ground from the rebellion. At the same time, his opponents, made up of ragtag citizen militias backed by mutinous army units, don't seem to have the capabilities to make a military move against territory still in regime hands.

Instead, the eastern-based opposition is hoping that residents of those areas _ including Tripoli _ will be able to rise up like they did in other cities where protesters drove out Gadhafi loyalists.

Friday could be a significant test of whether the opposition can maintain protests in Tripoli in the face of a fearsome clampdown.

Several hours before prayers, security forces began to take up positions. Internet services, which have been spotty throughout Libya's upheaval, appeared to be halted completely in Tripoli on Friday. In Tajoura, scene of protests last week, police set up two checkpoints on the main highway leading to downtown. They stopped cars to search them, check drivers' ID and ask where they were going or coming from.

Before noon prayers, worshippers massd in Tajoura's Murad Agha mosque, debating on what to do next. They said messages between Tripoli organizers were being aired on radio being aired from Benghazi, the main city in the opposition-held east, and audible in the capital.

At one point, they decided to hold a sit-in inside the mosque to avoid coming under gunfire by stepping outside.

"Gadhafi lies with impunity," said one 80-year-old among the worshippers, wearing traditional Libyan dress. "For 40 years, he never told the truth."

But in the end, the 400 worshippers inside marched out, joined by hundreds of others.

Some protests in other parts of the capital appeared to have not gotten off the ground. One resident said he went to prayers at a downtown mosque and found police officers standing outside to ensure no one marched. After prayers, the worshippers dispersed without protests.

The resident added that authorities distributed Thursday leaflets calling on people to gather after the Friday prayers in the Green Square to show support for the "Brother Leader," Gadhafi.

Libyan authorities briefly barred many foreign journalists from leaving their hotel in Tripoli, claiming it was for their protection because they had information "al-Qaida elements" plan to open fire on police to spark clashes. They later allowed them to go out into Tripoli.

Gadhafi loyalists in the capital have unleashed a wave of arrests and disappearances since last Friday's bloodshed. Bodies of people who vanished have been dumped in the street. Gunmen in SUVs have descended on homes in the night to drag away suspected protesters, identified by video footage of protests that militiamen have pored through to spot faces. Other militiamen have searched hospitals for wounded to take away.

Residents say they are under the watchful eyes of a variety of Gadhafi militias prowling the streets. They go under numerous names _ Internal Security, the Central Support Force, the People's Force, the People's Guards and the Brigade of Mohammed al-Magarif, the head of Gadhafi's personal guard _ and they are all searching for suspected protesters.

"While you are speaking to me now, there are spies everywhere and people watching me and you," one man said, cutting short a conversation with an Associated Press reporter visiting the Tripoli district of Zawiyat al-Dahman on Thursday.