A powerful explosion was reported at a foreign ministry building in the city of Benghazi, in northeastern Libya on Wednesday, on the first anniversary of an attack on the U.S. consulate in the city that killed four Americans, including the ambassador.

The blast caused severe damage to the foreign ministry building and to a nearby local headquarters of Libya's central bank, Agence France-Presse, or AFP, reported citing witnesses. However, it was not immediately known whether anyone was killed by the explosion, which witnesses, cited by AFP, said was apparently caused by a car bomb.

The attack comes at a time when the U.S. is struggling to bring to justice the perpetrators of the Sept. 11, 2012 attack on its consulate that killed four American diplomats including Chris Stevens, the ambassador to Libya. Although the U.S. has indicted suspects in the case, the Libyan government has rebuffed the U.S. administration’s efforts to arrest them.

Benghazi lies 630 miles to the east of Tripoli, the national capital, and in recent months, there has been an escalation in attacks against security forces, foreign diplomats and other western interests in the city, which is controlled by radical Islamic groups.