British Foreign Secretary Philip Hammond arrived Monday on a surprise visit to Tripoli, officials said, in the latest foreign visit in support of Libya's UN-backed unity government.

A media advisor for the Government of National Accord told AFP that Hammond would hold a news conference after talks with officials, as the GNA posted a picture on its website showing him meeting prime minister-designate Fayez al-Sarraj.

Hammond's visit comes as Libya's internationally recognised parliament, under pressure by the world community to endorse the GNA, was due to hold a crucial vote of confidence.

It also coincides with moves by the GNA to further assert its authority in the war-torn North African nation by taking control later Monday of three ministries.

The GNA would begin running the ministries of social affairs, youth and sports, and housing and public works, regardless of the results of the vote of confidence, its deputy Ahmed Maiteeq said Sunday.

The legislature's vote would be a key step for Sarraj's unity government which was formed under a UN-backed power-sharing deal in December to assert its authority.

Hammond is the latest European foreign minister to visit Libya after those of Italy, France and Germany.

Europe is increasingly alarmed by the expansion of the Islamic State group in Libya, where the jihadists have set up a bastion just 300 kilometres (185 miles) away from Italy across the Mediterranean.

Oil-rich Libya, which has been mired in turmoil since the 2011 NATO-backed uprising that ousted and killed dictator Moamer Kadhafi, is also looking to Europe for help in tackling terrorism, illegal migration and to train its army and police force.

"Mr Hammond is in Tripoli, he is meeting the Presidential Council (chaired by Sarraj) and will hold a press conference after the meetings," a media advisor for the GNA told AFP.