An Afghan soldier shot dead two U.S. soldiers and injured two others in Afghan capital Kabul, the U.S.- led coalition forces said in a statement received Monday.

The Afghan soldier fired shots into the U.S. soldiers' vehicles when they were leaving Pul-e-Charkhi prison on the outskirts of Kabul on Sunday, the statement said, adding two U.S. soldiers were killed and two others injured.

"Other Afghan soldiers providing external security for the prison rushed to the aid of the U.S. personnel and fatally shot the rogue soldier," the statement said.

The two wounded are listed in stable condition and the names of the killed soldiers were being withheld pending notification of next of kin.

It is unclear what motivation was behind the attack. "U.S. and Afghan officials are investigating this incident," said the statement.

A coalition spokesman said the attacked U.S. soldiers were working as mentors to Afghan forces guarding the prison.

Suspected Afghan terrorists transferred from the U.S. military prison at Guantanamo Bay, Cuba, are usually detained in Pul-e- Charkhi prison.

Source: Xinhua