MOSUL, Iraq, (Reuters) – A U.S. air strike killed eight Kurdish Peshmerga militiamen and wounded six others in northern Iraq, Kurdish officials said on Friday, describing the incident as an apparent act of friendly fire.

The U.S. military said in a statement that U.S. forces had killed five armed men in the northern city of Mosul early on Friday during a raid targeting an al Qaeda cell.

The men turned out to be Kurdish police, the statement said, adding that U.S. forces expressed their “deepest sympathies to the families of those individuals killed”.

Kabir Goran, deputy head of the Patriotic Union of Kurdistan (PUK), one of two main Kurdish political parties in Iraq’s autonomous Kurdistan region, said the air strike occurred around midnight on hursday when a U.S. helicopter attacked what he called a Kurdish Peshmerga watchtower in eastern Mosul. “We think they may have hit us by mistake,” Goran told Reuters.

The military statement said that during the operation, U.S. forces identified armed men from a bunker near the targeted al Qaeda building. Calls were made in Arabic and Kurdish for the men to put down their weapons.

As air support was called in, the statement said small arms fire came from the bunker.

Mosul lies close to the Kurdistan region. Kurdish militiamen have a presence in parts of the city.