The Libyan prime minister's chief of staff has disappeared and may have been abducted amid a series of confrontations between the government and fighters in the capital Tripoli, officials said.



The prime minister's office said in a statement on Monday that it had lost contact with Mohamed Ali Ghatous, who works for Prime Minister Ali Zidan, and was searching for him.



Officials said he went missing late on Sunday and his car was found on the side of the road on the outskirts of Tripoli the next day.



The officials say he may have been abducted, speaking anonymously in line with regulations.



Two years after the country's civil war, Libya is struggling to build a unified army and police force and reign in militias, which include many rebels who fought to oust the country's longtime dictator Muammar Gaddafi.



The government often depends on the militias to fill the security vacuum.



Recently, groups of fighters have taken offence at statements by ministers criticising the near impunity they enjoy in many parts of the country and suggesting they needed to be brought under control.



Ghatous' disappearance comes less than a week after Zidan was besieged in his office by fighters who demanded his ouster over remarks he made threatening to summon outside help to confront the armed groups.



On Sunday, the same day that Ghatous disappeared, dozens of fighters surrounded the justice ministry in a daylong siege and also called for minister Salah al-Marghani's resignation.



Al-Marghani had told a Libyan TV station that some of the fighters were illegitimate groups and were operating illegal prisons. He demanded that they relinquish control over them to the justice ministry.



Zidan and al-Marghani also held a joint news conference on Sunday, saying that fighters would be held accountable for any attacks.