The Foreign Office urged British nationals to leave Benghazi in Libya "in response to a specific, imminent threat to westerners".
At least 11 were killed and 60 wounded as demonstrators staged a 'rescue Benghazi' protest aimed at driving militants out of their city.
At least 4 were killed and 34 wounded as demonstrators staged a 'rescue Benghazi' protest aimed at driving militants out of their city.
Yesterday US Secretary of State Hillary Clinton said the Algerian militants involved in the attack on a desert gas plant had weapons from Libya.
"There is no doubt that the Algerian terrorists had weapons from Libya. There is no doubt that the Malian remnants of AQIM have weapons from Libya."
AQIM - Al Qaeda in the Islamic Maghreb - is an affiliate of al Qaeda.
Hillary Clinton was testifying before the Senate Foreign Relations Committee about the September attack by Islamist militants in which the US ambassador and three other Americans were killed in Benghazi.
The Prime Minister's spokesman reiterated the "specific imminent threat" to Westerners in Benghazi in Libya, which is why they have been urged to leave.
Although journalists were told there have been regional threats, we were told the Government does not talk about the details behind threats or the information received.
The spokesman would not confirm whether this threat was linked to the situation in Mali or Algeria.
Air Malta has cancelled its flights to Benghazi on Thursday following the Foreign Office's advice for Britons to leave.
In a statement on the website the airline said:
Whilst Air Malta regrets any inconvenience caused, the airline will always place the safety and security of its staff and customers as its highest priority.
British nationals have been advised to leave Benghazi in Libya, just a week after four Britons were killed in a terrorist attack in In Amenas, Algeria.
Foreign Office minister David Lidington, told the BBC that the risk of terrorism in the region has been ongoing for some time but that the Foreign Office would not issue its current advice to leave if there were not serious reason to do so.
The terrorism risk has been there for some time, before Mali and before the Algeria crisis of last week.
I cannot comment further on operational matters but the safety of Britons is our primary concern at the Foreign Office.
We only issue the kind of advice we have, to leave Benghazi, if we have information on a credible and imminent threat.
The Prime Minister's spokesman has reiterated the "specific threat" to Westeners in Benghazi., but would not say what that was, or whether linked to Mali and Algeria.
The Foreign Office spokesman said: "We cannot comment further on the nature of the threat at this time."
Benghazi was the stronghold of the Western-backed revolt that eventually ended Gaddafi's hold on power in Libya.
However, Britain has not had any diplomatic presence in the city since an attack on the US mission last September that killed American ambassador Chris Stevens and three of his colleagues.
The Foreign Office has been advising against travel to most of Libya since last September, but has now stepped up its warning.
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.
We have updated our travel advice to reflect this. The British Embassy in Tripoli has been in contact with British nationals for whom we have contact details to alert them to the advice.
The Foreign Office today urged British nationals to leave Benghazi in Libya "in response to a specific threat to westerners".