KABUL, Afghanistan - Afghan security officials have confirmed that at least four security forces were killed when their vehicle was attacked by a suicide bomber in the capital Kabul.

The security officials, who did not want to be named as the investigation into the attack is still underway, said Wednesday that 11 others were wounded in the attack which took place in Puli Mohmood Kahn area near the Afghan defense ministry compound.

They said it is not clear if the bomber was on foot or on a motorbike when he attacked the forces.

No any group has claimed responsibility for the attack, but Taliban insurgents have recently increased their attacks against Afghan security forces across the country.