A man wearing an Afghan army uniform has shot dead an American service member in southern Afghanistan, officials said Thursday.

It was the latest in a string of attacks against American and other foreign forces by Afghan troops or insurgents in disguise.

NATO said the shooter was killed Wednesday when coalition forces returned fire. It had no more immediate details but said the attack was under investigation.

The alliance didn't give the nationality of the slain service member, but a senior U.S. defense official said the person killed was an American. The official spoke on condition of anonymity as they were not authorized to release details.