"At 06:30 am, we received information that Camp Phoenix was under attack by small arms and RPGs," said the spokesman for the NATO-led International Security Assistance Force (ISAF).

"Early reports indicate that there were two attackers, one of which was a potential suicide bomber. Friendly forces returned fire and both were killed."

Three troops were slightly wounded, he added, without being able to specify whether they were foreign or Afghan.

Kabul police criminal investigation chief Mohammad Zahir confirmed the incident and said four attackers were killed.

"Four attackers were involved. Two of them blew themselves up against Camp Phoenix, one was shot dead and the fourth one, who wanted to flee wearing a burqa, was also brought down by the security forces. He died from wounds. They exchanged fire with the security forces."