Libya's deputy prime minister, Awad al-Barasi, resigned on Saturday, saying he was not given enough powers to carry out his duties.
"I cannot work in a dysfunctional government where my powers are lost," al-Barasi told a news conference in Benghazi.
Barasi criticized Prime Minister Ali Zeidan's Cabinet, saying it did not deal with problems in a real manner.
Zeidan said last week he would reshuffle the Cabinet and reorganise the government to cope with the urgent situation in the country following killings in the eastern city of Benghazi that sparked violent demonstrations.
The unrest was sparked by the assassination of a prominent political activist and critic of the Muslim Brotherhood, Abdelsalam al-Mosmary, who was shot dead after leaving a mosque in Benghazi.
Barasi is a member of the Muslim Brotherhood-linked Justice and Construction party.