A NATO helicopter called in to support Afghan police at a highway checkpoint opened fire and mistakenly killed five Afghan officers, authorities said Thursday, Aug 1, as international troops prepare to withdraw from the country.

The killings happened Wednesday night in eastern Nangarhar province's Bati Kot district, some 120 kilometers (75 miles) from the capital, Kabul. Police officers manning a checkpoint on a highway near the border with Pakistan came under fire and called in for air support from NATO troops, said Ahmad Zia Abdulzai, a spokesman for the provincial governor.

It's unclear what happened next, but the NATO helicopter opened fire on the Afghan troops, killing five soldiers, said Capt. Malloy Ebony, a spokeswoman for the U.S.-led International Security Assistance Force.

Ebony said NATO troops were responding to a call from helped from combined Afghan and NATO coalition troops. Lt. Col. Will Griffin, another ISAF spokesman, said that the operation in the area involved a combined force of international and Afghan troops, but gave no further details. That contradicted information initially provided by Afghan authorities about the incident. The different accounts could not be immediately reconciled Thursday.

"An investigation is being conducted at this time to determine this specific circumstances that lead to this," Ebony said.