Several people have been injured as opponents and supporters of a renegade ex-general clashed in the Libyan capital, Tripoli.
Witnesses told Al Jazeera that Friday's skirmishes in Martyrs' Square started with verbal insults and protesters throwing water bottles and sticks at each other.
After a tense stand-off, gunshots were heard, and protesters started running.
"We are against [ex-general Khalifa] Haftar and now they are shooting at us," a woman shouted as she ran by an Al Jazeera cameraman.
It was not clear who had opened fire and no one was injured by the shooting.
On May 16, Haftar launched an offensive in Libya's second city, Benghazi, aimed at eradicating militias that he called "terrorists". Fighting has since escalated and Libya has become increasingly divided.
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The country has been wracked by instability and violence since a NATO-backed revolt toppled and killed Muammar Gaddafi in 2011, and the government has failed to control the armed groups that fought against him.
Several protests have been held in Martyrs' Square over the last weeks but Friday was the first time the rallies turned violent.
A man who was in the square told Al Jazeera that "the square should be a place that symbolises Libya and all people".
"It suddenly erupted and there was gunfire," he said. "A group appeared out of nowhere carrying metal rods and sticks."
Police told Al Jazeera that anti-Haftar protesters had been granted permission to hold a rally. Meanwhile, there were calls on social media for supporters of the former general to come out for what they called a "decisive Friday".
Earlier in the day, a car bomb targeted Hashem Bashar, the man in charge of integrating Tripoli's militias into the police force. He escaped unharmed.
The explosion, which happened before dawn, caused extensive damage to his home and surrounding buildings.
"People here tell us it was a massive explosion and it was heard up to 20km away, " Al Jazeera's Stefanie Dekker, reporting from Tripoli, said. "There is nothing left of the car, and it caused major structural damage to this street."
Bashar said he had no idea of the identity or motives of the bombers.
"If there are people out there who don't want to build just institutions... and they attacked me because I represent the path to that, then we welcome death and anything they will try to do to foil our efforts," Bashar told Al Jazeera.
"There is no other option for Libya but to build the police force and the army. All the militias have to disband."
There was no claim of responsibility for the attack.
The eastern city of Benghazi, cradle of the uprising against Gaddafi, has become a stronghold for fighters blamed for a wave of deadly attacks on security forces.
Haftar accuses Congress of allowing "terrorists" to flourish in Libya and has vowed to "wipe them out", gaining support from much of the regular armed forces and nationalist militias. Other militias have lined up to oppose him, insisting his attacks amount to a "coup".