An Afghan employed at the U.S. Embassy attacked a CIA office in Kabul and shot dead an American Sunday evening, officials said.

There was a shooting incident at an annex of the U.S. Embassy in Kabul last night involving an Afghan employee, who was killed, the U.S. Embassy said in a statement Monday.

The attack can be termed a major security lapse as officials posted at the embassy undergo rigorous security scrutiny. The motive behind the attack is still unclear and it isn't known if the attacker was acting for the Taliban or because of personal reasons.

According to embassy spokesman Gavin Sundwall, the Afghan employee wasn't authorized to carry a weapon, and it wasn't clear how he got a gun into the secured compound.

After the explosion was heard, an Afghan National Army vehicle was passing. CIA-employed guards opened fire on the vehicle, thinking it had attacked them, according to a BBC source. Sources also told the BBC that two ANA soldiers, one CIA guard and one presidential guard were wounded.

The CIA station in Kabul, the agency’s largest outpost overseas, is a part of the U.S. Embassy complex.

With this attack, Kabul witnessed its third high-profile attack in a month. Two weeks ago, Taliban militants attacked the embassy in Kabul leaving 25 dead. Earlier this week, the chief of Afghanistan’s High Peace Council, Burhanuddin Rabbani, was killed in a suicide attack.