Bombs exploded outside two police stations in Libya's eastern city of Benghazi on Thursday and Britain temporarily cut staff at its embassy in Tripoli because of security fears.
The blasts, which caused damage but no casualties, were the latest signs of insecurity in Benghazi, the birthplace of the uprising that toppled Muammar Gaddafi in 2011.
The government has also struggled to keep order in the capital Tripoli, where the French embassy was bombed less than three weeks ago. Armed groups seized control of two government ministries a few days later to press demands on parliament and have refused to leave until the prime minister steps down.
"Given the security implications of the ongoing political uncertainty, the British Embassy is temporarily withdrawing a small number of staff," an embassy statement said, adding that the mission would continue to operate as usual.
A British embassy source said the decision was prompted by the ministry sieges, along with concerns that rival armed groups could clash at demonstrations organised in the capital.
On Thursday, the U.S. State Department issued a new travel warning for Libya and said it had ordered a number of U.S. government personnel to leave Tripoli for security reason.
The State Department said it "strongly advises against all but essential travel to Tripoli and all travel to Benghazi, Bani Walid, and southern Libya, including border areas and the regions of Sabha and Kufra".
More than two years after Gaddafi was slain, armed groups that helped topple him are still more powerful than the state in large swathes of the oil-producing North African desert country.
France, the United States and Britain, in an unusual joint statement on Wednesday, said Libyan institutions and elected representatives must be able to work free of armed intimidation.
"We call on all Libyans to refrain from armed protest and violence during this difficult time in the democratic transition," the three Western nations said.
The government turned to Europe's development bank on Friday for help in building institutions to fill the administrative vacuum left by more than four decades of Gaddafi's one-man rule.
For the time being, Libya is seeking only technical cooperation with the European Bank for Reconstruction and Development - a relatively low-level relationship with the bank.
But countries such as Egypt have gone on from this status to become full-scale recipients of investment from the bank - originally set up to help Europe's ex-communist states.
Libya is not short of cash, but lacks the institutions and processes for spending the vast oil wealth it has accumulated.
"The central bank governor said they have $130 billion in reserves but no state institutions," said a source close to Libya's discussions with the EBRD bank.