More than 1,000 inmates escape from Libyan prison.

Protesters in Benghazi hold a demonstration against the killing of lawyer and prominent political activist Abdul-Salam Al-Musmari. Photograph: Xinhua/Landov/Barcroft Media

More than 1,000 inmates have escaped from a prison in Libya as protesters stormed political party offices across the country.

It wasn't immediately clear if the jailbreak at al-Kweifiya prison on Saturday was connected to the demonstrations. Protesters had gathered across Libya over the killing of an activist who had been critical of the Muslim Brotherhood.

Inmates started a riot and lit fires after security forces opened fire on three detainees who tried to escape from the facility near Benghazi, a security official at the prison said. Gunmen quickly arrived at the prison after news of the riot spread, opening fire with rifles in a bid to free their imprisoned relatives.

Those who escaped either faced or were convicted of serious charges, the prison official said.

Special forces later arrested 18 of the escapees, while some returned on their own, according to Mohammed Hejazi, a government security official in Benghazi. The three inmates wounded in the initial escape attempt were taken to a local hospital, he said.

At a news conference, the prime minister, Ali Zidan, blamed the jailbreak on those living around the prison. "The prison was [attacked] by the citizens who live nearby because they don't want a prison in their region" he said. "Special forces were present and could have got the situation under control by using their arms but they had received orders not [to use] their weapons on citizens ... so the citizens opened the doors to the prisoners."

Zidan said an alert would be sent to border posts about the jailbreak and officers would receive a list of the escapees' names.

Benghazi's security is among the most precarious in post-revolution Libya. Last year, US ambassador, Chris Stevens, and three other Americans were killed in an attack on a US diplomatic mission in the city.

Meanwhile on Saturday, hundreds gathered in the capital, Tripoli, after dawn prayers, denouncing the Friday shooting death of Abdul-Salam Al-Musmari. They set fire to tyres in the street and demanded the dissolution of Islamist parties.

The two incidents highlighted Libya's deteriorating security situation and the challenges the north African country faces as it tries to restore calm nearly two years after the ousting and death of longtime dictator Muammar Gaddafi.