An American staff member of the U.S. Consulate in the eastern Libyan city of Benghazi has died following fierce clashes at the compound, Libyan security sources said early Wednesday.

"One American staff member has died and a number have been injured in the clashes," Abdel-Monem Al-Hurr, spokesman for Libya's Supreme Security Committee, told Reuters, adding that he did not know the exact number of wounded and could not say what the cause of death was.

Later Wanis al-Sharef, an Interior Ministry official in Bengazi, told the Associated Press the two victims had been shot. 

"We can confirm that our office in Benghazi, Libya, has been attacked by a group of militants," the State Department said in a statement. "We are working with the Libyans now to secure the compound. We condemn in strongest terms this attack on our diplomatic mission."

The State Department does not have independent confirmation of the death, an official told CNN. 

Earlier Tuesday, State Department spokeswoman Victoria Nuland said, "We are working with the Libyans now to secure the compound. We condemn in strongest terms this attack on our diplomatic mission."

Armed gunmen attacked the compound on Tuesday evening, clashing with Libyan security forces before the latter withdrew as they came under heavy fire. The armed group is said to have been protesting a film being produced in the United States.

The incident followed a protest in neighboring Egypt where demonstrators scaled the walls of the U.S. Embassy, tore down the American flag and burned it during a protest over what they said was a film that insulted Prophet Mohammad.

Reuters reporters on the scene could see looters raiding the empty Benghazi compound, walking off with desks, chairs and washing machines.

Unknown gunmen were shooting at the buildings while others threw handmade bombs into the compound, setting off small explosions. Small fires were burning around the compound.

Passersby entered the unsecured compound to take pictures with their mobile phones and watch the looting.

No security forces could be seen around the consulate and a previous blockade of the road leading to it had been dismantled.

"The Libyan security forces came under heavy fire and we were not prepared the intensity of the attack," Hurr said.

Suleiman El-Dressi, Al Jazeera's producer in Benghazi, said, "A group of people calling themselves the 'Islamic law supporters' heard the news that there will be an American movie insulting the Prophet."

"One they heard this, they came out of their military garrison and went into the streets calling upon people to gather and go ahead to attack the American Consulate in Benghazi."

Libya's interim government has struggled to impose its authority on a myriad of armed groups which have refused to lay down their weapons and often take the law into their own hands.

A number of security violations have rocked Benghazi, Libya's second biggest city and the cradle of last year's revolt that toppled Muammar Gaddafi.