The revelation was first reported by the New York Times, which has revealed in a series of articles this month that American troops handled an arsenal of deteriorating chemical agents and were sometimes told to stay silent about what they encountered.
The Pentagon failed to recognize the scale of the reported cases of exposure to chemical agents or to offer proper tracking and treatment to those troops who may have been injured, the Times wrote, citing defense officials.
US forces found no proof of an active program, but they did find remnants of an aging chemical stockpile that they were not well trained to handle, the newspaper reported.
The Times initially uncovered 17 cases of American troops who suffered damage from sarin or a sulfur mustard agent, and about eight more came forward.
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But a new review of military records ordered by Pentagon chief Chuck Hagel has now found that hundreds of troops informed the military they believe they were exposed, officials said, confirming the Times report.
Following the invasion that toppled Saddam Hussein, American forces uncovered 5,000 warheads, shells and bombs filled with chemical agents, but their findings were kept secret, according to the Times.