Britain is working with international partners on a co-ordinated rescue mission for the last foreign nationals stranded in Libya amid fast-deteriorating security conditions.

David Cameron discussed the plans with fellow European leaders hours before what is expected to be the last Government-chartered aircraft arrived in Tripoli to evacuate more Britons.

With most expatriates now safely extracted from the capital and other cities, attention has focused on around 170 UK oil workers stranded in remote and highly vulnerable desert locations.

SAS troops were understood to be ready to move in to evacuate those stuck in the oilfields, though the Ministry of Defence refuses to comment on the movements of Special Forces.

The Prime Minister's talks with his German and Italian counterparts also established agreement on the urgent need to impose "tough sanctions" against Muammar Gaddafi's regime.

A chartered Boeing 737 - with room for 148 people - touched down at Tripoli Airport on Saturday afternoon amid no sign of any abatement of the violence, described by some evacuees as a "living hell".

It is expected to take off for London's Gatwick Airport - where earlier another aircraft returned Britons who had been evacuated to Malta from Libya's second city Benghazi on board HMS Cumberland.

The Royal Navy frigate is returning to the port - which is in opposition hands - ready to help any others fleeing the bloody chaos in which at least 1,000 people are thought to have been killed.