Protesters attacked offices of Libya’s Muslim Brotherhood and the headquarters of a liberal coalition yesterday after demonstrations sparked by assassinations in the eastern city of Benghazi turned violent, witnesses said.

Hundreds took to the streets overnight to denounce the killing of a prominent political activist and critic of the Brotherhood, Abdelsalam al-Mosmary, who was shot dead on Friday after leaving a mosque.

Mosmary, one of the first activists who took to the streets in Libya’s February 2011 uprising, was an outspoken opponent of the Brotherhood, whose Islamist political wing is the second biggest party in Libya’s General National Congress (GNC). Two military officials were also killed in Benghazi on Friday.

Protesters in Benghazi invaded and set fire to a building housing the Muslim Brotherhood’s political wing

Libya’s government is struggling to assert its authority over armed groups that helped topple veteran leader Muammar Gaddafi in 2011, part of the wave of Arab Spring uprisings that also felled autocrats in Tunisia, Egypt and Yemen.

Protesters in Benghazi invaded and set fire to a building housing the Muslim Brotherhood’s political wing, the Justice and Construction Party (JCP), witnesses said.

“They shouted ‘Gather your belongings. Benghazi wants you out’,” Benghazi resident Rami al-Shahibi said.

Hundreds later gathered outside Benghazi’s Tibesti hotel, one of the main squares in the city for demonstrations, for funeral prayers for Mosmary before heading to a cemetery. They continued to shout anti-Brotherhood slogans.

In Tripoli, a crowd stormed JCP headquarters before heading on to ransack the headquarters of the liberal National Forces Alliance (NFA), the country’s biggest political party founded by wartime rebel prime minister Mahmoud Jibril.

There has been rising opposition in Libya to the influence of the Muslim Brotherhood, which has links to several government ministers.

The movement has struggled to convince Libyans that it has no financial or administrative links to its namesake in neighbouring Egypt, whose Islamist president Mohamed Mursi was overthrown by the army on July 3. Many of the protesters accused the Brotherhood of being behind the killings in Benghazi, cradle of the 2011 revolution and now a hotspot for violence – a charge rejected by Abdulrahman al-Dibani, a JCP member in congress.

“We have strongly condemned the assassination of Mosmary,” he said.