BENGHAZI, Libya >> Militias loyal to Moammar Gadhafi opened fire today trying to break up marches by regime opponents defying a fierce clampdown to hold their first major protest in the Libyan capital Tripoli in days. Across rebellious cities in the east, tens of thousands held rallies in support of the Tripoli protesters.

Protesters chanting for Gadhafi’s ouster streamed out of mosques in downtown Tripoli after prayers, and they were confronted by a force of troops and militiamen who opened fire in streets near Green Square, said several witnesses.

One man in the Souq al-Jomaa area near the square reported seeing dead or injured from the gunfire. “There are all kind of bullets,” he said, screaming in a telephone call to The Associated Press, with the rattle of shots audible in the background. He could not say how many casualties he saw, and his report could not immediately be confirmed.

“The situation is chaotic in parts of Tripoli now,” said another witness, who was among marchers in adjacent Algeria Square and said he saw militiamen firing in the air. Armed Gadhafi supporters were also speeding through some streets in vehicles, he said. Residents hiding in their homes also reported the sound of gunfire in other parts of the capital.

The call for regime opponents march from mosques after prayers was the first attempt to hold a major anti-Gadhafi rally in the capital — the Libyan leaders biggest remaining stronghold — since bloody clashes Tuesday night. SMS messages were sent around urging, “Let us make this Friday the Friday of liberation,” residents said. The residents and witnesses all spoke on condition of anonymity for fear of retaliation.

Starting this morning, Gadhafi militiamen set up heavy security around many mosques in the city, intimidating opposition worshippers. Armed young men with green armbands to show their support of Gadhafi set up checkpoints on many streets, stopping cars and searching them. Tanks and checkpoints lined the road to Tripoli’s airport, witnesses said.

Thousands of protesters marched after prayers in Tajoura, a crowded impoverished district on the eastern side of the capital. One participant said they intended to head to Green Square downtown. The district has been the scene of clashes on previous nights, and at one point residents raised the old pre-Gadhafi flag of Libya’s monarchy in the streets, the symbol of the uprising against the Libyan leader.

Tripoli, home to nearly a third of Libya’s 6 million people, is the center of the territory that remains under Gadhafi’s control after the uprising that began Feb. 15 swept over nearly the entire eastern half of the country, breaking cities there out of his regime’s hold.

Even in the pocket of northwestern Libya around Tripoli, several cities have also fallen into the hands of the rebellion. Militiamen and Gadhafi forces on Thursday were repelled in trying to take back territory in the cities of Zawiya and Misrata in fighting that killed at least 30 people.

Several tens of thousands held a rally in support of the Tripoli protesters in the main square of Libya’s second-largest city, Benghazi, where the revolt began and which is now part of the opposition-held territory in the east.

Muslim cleric Sameh Jaber led the prayers in the squares, telling worshippers that Libyans “have revolted against injustice.”

“God take revenge from Moammar Gadhafi because of what he did to the Libyan people,” the cleric, wearing traditional Libyan white uniform and a red cap, said in remarks carried by Al-Jazeera TV. “God accept our martyrs and make their mothers, fathers and families patient.”