Britain on Thursday said it was aware of a "specific and imminent" threat to Westerners in the Libyan city of Benghazi and urged British nationals to evacuate, giving no details of the nature of the danger.
An attack on the US mission in the eastern city in September last year killed four Americans, including the US ambassador, part of a wave of violence targeting foreign diplomats, military, and police officers.
"We are now aware of a specific and imminent threat to Westerners in Benghazi, and urge any British nationals who remain there against our advice to leave immediately," the Foreign Office said in a statement.
The Foreign Office declined to give more details about the nature of the threat in the city, cradle of the 2011 revolution that toppled former Libyan leader Muammar Qaddafi.
Libya has been awash with weapons since then, and its shaky nascent institutions have struggled to rein in armed groups keen on ensuring they receive what they see as their fair share of power for helping to oust Qaddafi.
Benghazi in particular has been the scene of power struggles between various armed Islamist factions.