Updated

The Pentagon says that an Islamic State rocket that hit a military base used by hundreds of U.S. troops in northern Iraq did not contain any sulfur chemical agent, as initially feared.

U.S. officials had said that an oily substance found on a fragment of the rocket that landed inside the security perimeter of Qayara West air base last week initially tested positive for a rudimentary form of mustard agent, but subsequent tests came back negative and inconclusive.

Navy Capt. Jeff Davis said that follow-up tests were done and the ultimate conclusion is that it was not sulfur mustard.

Last week Marine Gen. Joseph Dunford, chairman of the Joint Chiefs of Staff, told a Senate Armed Services Committee hearing that the military assessed it to be a sulfur-mustard blister agent.