Kabul: An Afghan employee of the US government opened fire inside a CIA office in Kabul on Sunday evening, killing an American and injuring a second, US and Afghan officials said, in the second major breach of embassy security in two weeks.

The killing adds to a sense of insecurity already heightened by a 20 hour-siege of the embassy district in mid-September, and the assassination a week later of the government's peace envoy, former President Burhanuddin Rabbani.

The CIA compound is one of the most heavily guarded in Kabul, and has been off-limits for almost a decade, since shortly after the Taliban's fall from power in 2001. It also lies at the heart of the capital's heavily-guarded military, political and diplomatic district, a virtual "green zone" that is almost impossible for ordinary Afghans to enter.

It was not clear if the US citizens were victims of a rogue employee who had been won over to the insurgent cause, or just the escalation of an argument in a city where tensions are high and many people carry guns. There are precedents for both.

Lone attacker

The "lone attacker" was killed, and the injured US citizen was taken to a military hospital, US embassy spokesman Gavin Sundwall said yesterday.

"There was a shooting incident at an annexe of the US embassy in Kabul last night involving an Afghan employee who was killed. The motivation for the attack is still under investigation at this time," Sundwall said. The shooting follows a string of attacks by Afghan security forces against their Nato-led mentors carried out either by "rogue" soldiers and police or by insurgents who have infiltrated security forces.