Earlier Sunday, a security official said the deputy intelligence chief was abducted as he left Tripoli's airport. It was not clear who abducted Mustafa Nouh, whose family is originally from Misrata.
Public anger had been directed at the militias from Misrata, who had developed a strong presence in the capital following the fall of longtime dictator Moammar Gadhafi in 2011.
Except for several protests, streets were deserted as the vast majority of Tripoli's businesses and schools were closed, with bakeries, pharmacies, hospitals and gas stations the main exception. The head of Tripoli's city council, Al-Sadat al-Badri, said the strike is to last three days.
Fearing renewed violence, armed residents have set up checkpoints to protect their neighborhoods.
On Sunday, nearly a hundred protesters entered the parliament building while lawmakers were in session, demanding legislation to disband the militias and forcing the session to break up.
Lawmaker Fatma al-Misbari said the interim parliament was under strong pressure, but it did not specify from whom.
"There is no consensus. There is pressure on the council and the government," she said at the parliament building.
Libya's militias originated in the "revolutionary" brigades that fought against Gadhafi's forces in 2011. Since his ouster and death, they have refused to disarm and have grown in size and power. Many have been enlisted by the state to serve as security forces, since the army and police remain weak, underequipped and underpaid. But many continue to act as armed vigilante factions with their own interests, sometimes turning political feuds into armed conflicts.
Too weak to disarm the militias, the military, police and government have tried to co-opt them, paying them to take on security roles such as guarding districts, facilities, and even polling stations during elections. But the policy has backfired, empowering the militias without controlling them.
At the parliament, protesters carried a coffin draped in Libya's post-Gadhafi flag and held posters declaring those killed in the recent violence to be "martyrs of dignity."
Speaking to Libya's Al-Ahrar TV, Ali Azouz said the protesters had entered the building to demand that legislators order the disbanding of militias and their removal from Tripoli.
"We were revolutionaries since (the start of the 2011 uprising) but when we were asked to hand back our weapons we did so and went back to work," Azouz said, denouncing the existence of the armed groups.
Libya's state news agency LANA said Sunday that the Misrata militias accused of being responsible for Friday's killings in the southern Tripoli neighborhood of Gharghour had abandoned their bases there. The militias had turned villas and residential compounds of former Gadhafi-era officials into camps where they stashed weapons.
It is not clear where the Misrata militias went.
A government-affiliated militia, the Libya Shield-Central Command, announced late Saturday that it had taken control of Gharghour, declaring it a military zone and vowing to turn it over to the government. The majority of Libya Shield's militiamen also hail from Misrata.
Many Tripoli residents also marched in protest against Libya Shield's takeover of Gharghour.
"No to Libya Shield-Central Command," hundreds chanted Sunday, demanding the group hand over the neighborhood to the military or police.