KABUL, Afghanistan - Insurgents stormed a police post in southern Afghanistan early Thursday, killing four officers and wounding two others in their sleep, officials said.

Police and local government officials accused a rogue member of the Afghan National Police of aiding the attack, which took place about 4 a.m. in the Oruzgan provincial capital, Tarin Kot.

The suspect, identified as a recruit named Hayat Khan, allegedly contacted Taliban militants when he was about to come off his shift to inform them that his colleagues were sleeping, police spokesman Farid Ayel said.

Police are searching for the suspect, who disappeared after the attack.

"We are not sure yet whether Hayat Khan has defected to the Taliban or fled the province," said provincial government spokesman Abdullah Hemat.

Another suspect, who was believed to have been facilitating communication between Khan and the Taliban, has been detained for questioning, Ayel said.

Infiltration of the Afghan security forces by insurgents has become a major challenge for the government and international forces. Afghan soldiers and police - or insurgents dressed in Afghan uniforms - have killed at least 61 foreign troops and contractors this year, according to the NATO force.

The numbers don't include an attack Monday in which a policewoman is accused of shooting to death an American civilian contracted to support the Afghan police and Interior Ministry in the capital, Kabul. That killing is still under investigation, a NATO force spokesman said.

Government officials could not immediately provide figures on the number of Afghan casualties from insider attacks, but they have taken a toll. On Sunday, a member of the Afghan Local Police force in the northern province of Jawzjan was reported to have killed five other officers under his command before defecting to the Taliban.