Story highlights The convoy returned fire in self-defense and there were no US casualties

Monday's attack comes just days after three US soliders were killed and another wounded

Washington (CNN) A convoy carrying US and Afghan forces was struck by a roadside bomb and came under small arms fire in Afghanistan's Nangarhar province on Monday.

The convoy returned fire in self-defense and there were no US casualties, according to a NATO press release.

But Monday's attack comes just days after three US soldiers were killed and another wounded during a joint US-Afghan military operation in the same region.

An American official said the soldiers were shot in an apparent insider attack, also known as a " green-on-blue " incident because of the color-coding system used by NATO. During such assaults, members of the Afghan security forces are known to target US and other NATO soldiers.

Taliban spokesman Zabiullah Mujahid said the militants claimed responsibility for the attack.

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