Afghans working with international forces and the Afghan government are regularly targeted by the Taliban [Reuters]

A government prosecutor in southern Afghanistan has been killed by gunmen on motorcycles, Afghanistan officials said.

Mohammad Azam, the chief prosecutor for Helman province's Gereshk district was shot on Sunday morning as he was on his way to work, said Khushahal Shapa, Helmand province's attorney general.

Security forces are searching for the attackers, governor of Helmand's office said in a statement.

No one immediately claimed responsibility for the attack, but the Taliban regularly targets Afghans working with international forces or the Afghan government.

In eastern Afghanistan, the Taliban claimed responsibility for shooting down a NATO drone aircraft in the city of Jalalabad.

But a NATO spokesman, Captain Pietro D'Angelo of the Italian army, said initial reports indicated that the drone went down because of a mechanical failure.