The party wanted to censure Prime Minister Ali Zeidan
Libya’s Justice and Construction Party, the second largest party in the interim administration, has announced it is quitting the government.
The Islamist party said its five ministers would resign after it failed to win sufficient support for a motion to censure Prime Minister Ali Zeidan.
Those affected include the ministers for oil, the economy and housing.
The Justice and Construction Party is the political arm of the Muslim Brotherhood in Libya.
The party has been trying for weeks to secure the 120 votes it needed to bring a vote of no confidence against Mr Zeidan and his cabinet.
But it was only able to secure the signatures of 99 MPs.
“Zeidan failed in his duty to provide security, and to deliver in the electricity and oil sectors,” Nizar Kawan, a leading party member, said in a statement.
“We had asked for a withdrawal of confidence, but some don’t understand the danger of the stage we are at now.”
Libya’s interim administration had representatives from the two most prominent blocs in Congress – the Alliance of National Forces led by former Prime Minister Mahmoud Jibril, and the Justice and Construction Party.
When he initially chose his cabinet, Mr Zeidan said he tried to strike a balance between Libya’s different regions.
Correspondents say the resignations will deepen the deadlock in the interim parliament, which has so far made little progress due to political infighting.