Gunmen have killed a US citizen working at an international school in the Libyan city of Benghazi, medical and security sources said.

The attackers shot the American man, a chemistry teacher on Thursday morning while he was exercising, security services spokesman Ibrahim al-Sharaa said.

"He was doing his morning exercise when gunmen just shot him. I don't know why. He was so sweet with everyone," the school's director, Adel al Mansouri said.

The 33-year-old teacher was shot in the central Al-Fwihet neighbourhood and was later brought to the Benghazi Medical Centre.

He had been working at the international school since late last year.

No one has claimed responsibility for the shooting.

But Libyan special forces in Benghazi have been battling armed fighters from Ansar al-Sharia.

US officials blame the group for the September 2012 attack on the US consulate that killed the US ambassador to Libya and three other Americans.

Libya's armed forces have struggled to control rebel groups since NATO-backed uprisings ousted Muammar Gaddafi two years ago.


Source: Agencies