TRIPOLI (AFP) - Gunmen on Monday demanded the Libyan government's resignation as they besieged ministries despite the adoption of a law to purge officials from the regime of dead dictator Muammar Gaddafi from their posts.

"We are determined to continue our movement until the departure of (Prime Minister) Ali Zeidan," said Osama Kaabar, a leader of the militias who had promised to lift their siege if the law was passed.

The General National Congress, under pressure from the gunmen, on Sunday voted through the controversial law to exclude former Gaddafi regime officials from public posts in a move that could see the premier removed from office.

An AFP correspondent reported that armed men in vehicles equipped with machineguns and anti-aircraft guns still surrounded the foreign and justice ministries on Monday.

"The adoption of the law on political exclusion is a major step in the right direction. But we will take our time to examine certain aspects of the law," said the militia leader.

"On the other hand we are determined to bring down the government of Ali Zeidan," he said, accusing the premier of "provoking the thuwar", former rebels who fought Gaddafi's forces during the 2011 armed uprising.

Mr Zeidan's government launched a campaign a few weeks ago to remove the militias from the capital Tripoli.