Assailants attacked an Islamist party office in Tripoli and a soldier was killed in fighting in Libya's eastern city of Benghazi, officials said, in a wave of unrest since the killing of a political activist last week.

The death of prominent Muslim Brotherhood critic Abdelsalam al-Mosmary, shot after leaving a Benghazi mosque on Friday, has triggered violent demonstrations, with attacks on the movement's offices in Benghazi and Tripoli.

On Sunday, buildings used by the judiciary in Benghazi were bombed, followed by overnight clashes between an armed group and military special forces.

Violence and lawlessness, much of it involving former rebel groups, has hobbled governance in swathes of the North African oil producer since the war that toppled Muammar Gaddafi in 2011.

Early on Monday an unidentified group attacked the headquarters in Tripoli of the al-Watan (Nation) political party, led by former Islamist militia leader Abdelhakim Belhadj.

"They smashed windows, shot at the door locks to open them and threw Molotov cocktails inside," Jamal Ashour, head of the party's political office, told Reuters.

"The damage is serious. No one was injured."

"COLLAPSE OF A WHOLE NATION"

Fighting erupted overnight in Benghazi's western Gwesha district, hours after Sunday's bombings, in which 43 people were wounded, according to state news agency LANA, citing the health minister. Demonstrators later took to the streets to denounce the violence and voice their discontent with the government.

"Clashes broke out between special forces and an unknown armed group," Mohammed al-Hijazy, a spokesman for Benghazi security operations, said by telephone. "At least one soldier was killed. The special forces have now retaken control."

The cradle of the uprising against Gaddafi, Benghazi was also the scene of a mass jail break on Saturday.

"This escalation (of violence) will lead to a collapse of a whole nation. We need solidarity of the people," Prime Minister Ali Zeidan told reporters.

Facing increasing discontent over the state's inability to curb violence, Zeidan has said he will reorganise the government to cope with the "urgent" situation in Libya.

"People think the state is weak but the state does not even exist," he said. "Even if you brought the best politician from America or Europe, he will find himself helpless here."

In the jail break, 1,117 inmates escaped during a riot in Kuafiya prison on the outskirts of Benghazi. Officials said on Sunday that about 100 prisoners had been recaptured.

Violence has plagued Benghazi since last year, with attacks on security forces as well as foreign targets, including an assault on the U.S. mission in September in which the U.S. ambassador and three other Americans were killed.