KABUL, Afghanistan (AP) — An apparent friendly fire incident has killed five Americans troops in southern Afghanistan.

That’s according to a U.S. defense official who would provide no other details. An Afghan official said it happened in southern Zabul province.

A statement from NATO says the casualties happened during a “security operation” after the soldiers “came into contact with enemy sources.” A senior police official said the coalition soldiers may have been killed when they called for close air support.

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

In 2002, four Canadian soldiers were killed when an American F-16 jet fighter dropped a bomb on a group near a night firing exercise in southern Kandahar.

Copyright 2014 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.