Britons living in Libya should leave the country immediately because of the "greater intensity of fighting," the Foreign and Commonwealth Office (FCO) has warned.
The department warned that violent clashes between armed groups are possible across the country, including in the country's capital Tripoli, particularly at night.
They said: "Fighting can break out in many places and at short notice. It can become serious quickly putting those in the area at risk. You should remain vigilant at all times."
They added: "Keep a low profile and try to limit travelling around as much as possible, particularly at night. There is a high threat from crime."
There are believed to be between 100 and 300 Britons in the north African country.
Tripoli International Airport was closed a fortnight ago following clashes between armed groups nearby, but any Britons remaining should use "commercial means" to leave, they said.
The British Embassy remains open but with reduced staff and a limited ability to provide consular assistance.
More top news
Video shot in Islamic State capital Raqq purportedly shows at least two of three missing London schoolgirls.
Visitors were evacuated from a rollercoaster at Alton Towers after a power cut forced the ride to grind to a halt.