WASHINGTON — The United States shut down its embassy in Libya on Saturday and evacuated its diplomats to neighboring Tunisia under U.S. military escort amid a significant deterioration in security in Tripoli as fighting intensified between rival militias, the State Department said.

“Due to the ongoing violence resulting from clashes between Libyan militias in the immediate vicinity of the U.S. Embassy in Tripoli, we have temporarily relocated all of our personnel out of Libya,” spokeswoman Marie Harf said.

The withdrawal underscored the Obama administration’s concern about the heightened risk to American diplomats abroad, particularly in Libya where memories of the deadly 2012 attack on the U.S. mission in the eastern city of Benghazi are still vivid and the political uproar over it remain fresh ahead of a new congressional investigation into the incident.

The evacuation was accompanied by the release of a new State Department travel warning for Libya urging Americans not to go to the country and recommending that those already there leave immediately.

“The Libyan government has not been able to adequately build its military and police forces and improve security,” it said. “Many military-grade weapons remain in the hands of private individuals, including antiaircraft weapons that may be used against civilian aviation.”