Libya's foreign minister Moussa Koussa is making a surprise visit to London from Tunisia, according to Tunisia's official TAP news agency.

A Libyan government spokesman said Mr Koussa - in his post for two years - had not defected, but was travelling abroad on a diplomatic mission.

Mr Koussa flew out of Djerba airport bound for the UK on Wednesday afternoon, the Tunisian report says.

It comes as the UK takes steps to expel five Libyan diplomats.

Foreign Secretary William Hague told MPs the five, who include the military attache, "could pose a threat" to UK security.

The Foreign Office has said it is unaware of Mr Koussa's visit.

The development comes as rebels fighting Libyan government forces are continuing to lose ground and are retreating from their former strongholds along the eastern coast of Libya.

Earlier, Prime Minister David Cameron said the UK was not ruling out providing arms to rebels in "certain circumstances" but no decision had been taken.

The UK has been involved in more than 160 aerial missions, as well as missile strikes, over Libya since coalition operations began on 19 March following a UN resolution.

The coalition military action is aimed at enforcing a no-fly zone over Libya and protecting civilians from attacks by forces loyal to its leader Col Muammar Gaddafi. It has denied air strikes are meant to provide cover for a rebel advance.

Posted in: but was travelling abroad on a diplomatic mission,Libyan government spokesman said Mr Koussa - in his post for two years - had not defected