WASHINGTON (AP) — A U.S. defense official says five NATO service members who were killed in southern Afghanistan were American.

The official insisted on anonymity because he was not authorized to speak on the matter by name. This official referred to earlier statements issued by the international coalition for additional details.

The international coalition said Tuesday the service members were killed in an apparent friendly fire incident. The statement said all five soldiers died on Monday but did not give further details on the attack or the nationality of the soldiers.

If confirmed, it would be one of the most serious cases involving coalition-on-coalition friendly fire during the nearly 14 year Afghan war.

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