An Afghan employee of the United States Embassy in Kabul killed one U.S. citizen and wounded another in an attack on a CIA office inside the embassy annex Sunday, a U.S. Embassy statement said.

According to the statement, Sunday night’s attack was carried out by an Afghan employee of the U.S. Embassy, who was also killed in the shooting. But the statement didn’t provide any further information on the identity of the shooter and the two Americans.

The wounded embassy employee, whose injuries were described as “non-life threatening,” was evacuated to a military medical facility.

The shooting was first heard some time around 9:30 pm local time in an area known as the green zone, where many important foreign and Afghan facilities, including the U.S. Embassy, ISAF headquarter and the presidential palace, are located.

Initial reports indicated that the shooting was inside the heavily protected Ariana Hotel, the Central Intelligence Agency’s main station, a few blocks from the presidential palace. Later the U.S. Embassy announced that the shooting had taken place in one of the annex buildings of the embassy.

It is still unclear whether the attack on the embassy annex was a terrorist act or if it was caused by a simple argument between the Afghan shooter and his American victims.

"The motivation for the attack is still under investigation," the embassy statement said.

No group has claimed responsibility for the attack. The Taliban, the main insurgent group, didn’t say anything about the shooting and the group’s spokesmen could not be reached by phone.

Kabul, a one-time relatively safe capital of the country, has been targeted frequently by insurgents over the last couple of weeks. Sunday’s attack came less than two week of another high profile attack on the U.S. Embassy when a group of six insurgent took over a nearby high-rise building and showered rocket-propelled grenades and assault rifles on the embassy, ISAF headquarter and Afghan government facilities.

The attack lasted for 20 hours, 7 civilians were killed and many were injured. The Americans blamed the Haqqani Network, a ruthless insurgent group fighting NATO and Afghan forces, and accused Pakistan’s military spy agency the Inter Service Intelligence — or ISI — of supporting the group.

The attack came less than a week after the assassination of Burhanuddin Rabbani, Afghanistan’s top peace negotiator, in his residence by a suicide bomber, who was hiding explosive in his turban. Mr. Rabbani was leading a government effort to broker peace with the Taliban.

Yesterday the National directorate of security, Afghanistan’s main spy agency, announced that some arrests have been made in connection with Mr. Rabbani’s assassination.

(Zohori is a McClatchy special correspondent in Afghanistan)