Libya unrest: David Cameron apology for UK response

However, there is particular concern for some British oil workers thought to be stranded in isolated desert camps.

They are struggling to make contact because the phone networks have been disrupted and their supplies of food and water from Libyan cities are running out.

“Some we know have been subjected to attacks and looting. They are in a perilous and frightening situation,” said Mr Hague.

Tony Blakeway told the BBC he was at a camp in Amal with 300 people, about 50 of them British. He said armed locals had been protecting them but they were worried they would leave.

“Please send immediate help as these looters will be back here tonight. The phones are not working. Please help us to get out,” he said.

After a week of upheaval in Libya, protesters backed by defecting army units are thought to have almost the entire eastern half of Libya under their control.

The country’s beleaguered leader Col Muammar Gaddafi, who has been in power for 42 years, has vowed to fight to his “last drop of blood” rather than leave the country.

Earlier, Mr Hague told the BBC the “odds were stacking up” against Col Gaddafi, adding: “We have a government, or the remnant of a government, here which is prepared to use force and violence against its own people.”

He said the Libyan leadership would be “held to account” for crimes against its people.