( CNN ) -- A car bomb exploded outside a Foreign Ministry building in the Libyan city of Benghazi Wednesday , state media said , on the anniversary of an assault on the U.S. Consulate there that killed four Americans , including Ambassador Christopher Stevens . The blast did not cause any casualties but blew away large parts of the building 's facade , said Col. Abdullah Al Zaydi , spokesman for the Joint Security Task Force in Benghazi , according to Libya 's state news agency , LANA . Al Zaydi said the explosion was very powerful and destroyed the vehicle used for the bombing , which contained a large quantity of explosives , the news agency said . The blast also damaged a branch of the Central Bank of Libya and slightly injured one of its security guards , the bank said . The branch director , Abdel Qader Mohammed , said the explosion caused `` material damage '' to the building , but its computer systems were not affected . Fast facts : The Benghazi Consulate attack . Benghazi resident Sami Berriwen told CNN he heard the blast in the eastern city at about 7 a.m. Berriwen , a university student , said that if the explosion had happened just an hour later , the street would have been full of people . He said most Benghazi residents walk the street to get to school and to work , but because it was early , no one was out yet . Berriwen said he saw a fire truck but no casualties or ambulances at the scene . Diplomatic missions and security officials have repeatedly been the targets of attacks in Benghazi , leading most Westerners to leave . In January , gunmen targeted the car of the Italian consul general in Benghazi , but no one was injured . Bomb attacks also occurred last year on a U.N. convoy , as well as on a convoy carrying the British ambassador . In November , unknown gunmen assassinated the city 's temporary security director . Other towns and cities , including the capital , Tripoli , have also seen frequent attacks . In recent days , scores of U.S. Marines were moved closer to Libya to help beef up security before of the 12th anniversary of the 9/11 terrorist attacks on the United States and the first anniversary of the attack on the Benghazi consulate . Two U.S. officials told CNN on Monday that 250 combat-ready Marines had moved from their base in Moron , Spain , to the U.S. naval installation at Sigonella , Italy . That would enable them to reach Tripoli in three to four hours in the event of a crisis . Other U.S. forces are helping boost security at various embassies in the region , since the period around September 11 is seen as a time of greater threat to U.S. interests . The attack at the Benghazi compound has been a political flashpoint in a long-running battle between the administration and Republicans , who accuse it of not bolstering security before the attack , of botching the response to it and of misleading the public for political gain before the November 2012 election . A report by the U.N. secretary-general on the U.N. Support Mission in Libya , released this month , highlights the continuing security concerns and political polarization in Libya following the overthrow of strongman leader Moammar Gadhafi in 2011 . The status of the revolutionary fighters who helped to oust Gadhafi remains unclear , the process of transitional justice is almost stalled , the country 's borders are leaky and there are many unsecured weapons , adding to the instability , it said . `` The continuing volatile security situation in Libya in general , and in the eastern and southern parts of the country in particular , is a source of grave concern , '' it said . `` Targeted political assassinations , criminal activity and attacks and threats against the diplomatic community continue to plague the country , including Tripoli . The protection of the civilian population and the enforcement of law need to be reaffirmed as a national priority . '' CNN 's Barbara Starr contributed to this report .
Official says the powerful explosion was caused by a car bomb -- state media . The blast hit central Benghazi on the anniversary of the attack on the U.S. Consulate . The explosion damaged a Foreign Ministry building and a bank branch , a witness says . The Central Bank of Libya says one of its security guards was slightly injured .