Updated

The U.S. military says a rocket that landed within several hundred yards of U.S. troops at a base in northern Iraq may have contained mustard agent.

No one was hurt in the attack on Qayara West air base, according to a U.S. military official who discussed details on condition that he not be identified. Several hundred U.S. troops are on the base.

The official says the attack Tuesday was militarily insignificant. He says a small group of U.S. soldiers who inspected remnants of the rocket found a black, oily substance on a fragment of metal. An initial test of the substance showed it contained residue of mustard agent, but a second test was negative.

The fragment has been sent to a laboratory for further testing.