More than 1,000 detainees have escaped from a prison near the eastern Libyan city of Benghazi in a massive jailbreak, as protesters stormed the offices of political parties in Libya's main cities.

It was not immediately clear if Saturday's jailbreak at the Al-Kuifiya prison came as part of the protests or if inmates received outside help.

Protesters had massed across the country angry over the killing of an activist critical of the country's Muslim Brotherhood group.

"There was a riot inside Al-Kuifiya prison, as well as an attack from outside. More then 1,000 prisoners escaped," the official said on Saturday, asking not to be named.

"Special forces called in as reinforcements were given orders not to fire at the prisoners."

Turmoil 'exploited'

Suleiman El-Dressi, a journalist in Benghazi, told Al Jazeera that according to security sources, "the prisoners exploited the turmoil that was happening in the city and tried to escape".

"Three were shot dead, and the othes managed to get away."

The official said most of the escapees were common law detainees, including nationals of other African states.

"But some of them were detainees in cases linked to the former regime of Muammar Gaddafi," he said.

Several were recaptured shortly after the breakout.

Prime Minister Ali Zeidan confirmed the incident, without giving the number of fugitives.

"Residents of the area carried out the attack because they don't want the prison near their homes," he said, adding that border posts had been alerted and given a list of names to apprehend the escapees.

Zeidan earlier announced that border posts with Egypt had been closed to prevent the escape of the killers of a prominent activist in the eastern Libyan city on Friday.

Benghazi's security situation is among the most precarious in post-revolution Libya.

Last year, the US ambassador and three other Americans were killed in an attack there.

Meanwhile on Saturday, hundreds gathered in the capital Tripoli after dawn prayers, denouncing the Friday shooting death of activist and lawyer Abdul-Salam Al-Musmari.

They set fire to tires in the street and demanded the dissolution of Islamist parties.

The two incidents highlighted Libya's precarious security situation and the challenges the North African country faces as it tries to restore security nearly than two years after the ouster and killing of longtime leader Gaddafi.

Al Jazeera