FORT BLISS, Texas (AP) — Eleven soldiers were sickened — including two who were in critical condition — after ingesting an unauthorized substance during a field training exercise at Fort Bliss in Texas, U.S. Army officials said Friday.

All 11 soldiers are being treated at William Beaumont Army Medical Center in the border city of El Paso, where they have been since Thursday afternoon, Fort Bliss said in a statement. Those sickened include one warrant officer, two noncommissioned officers and eight enlisted members, the statement said.

The soldiers "fell ill after consuming a substance acquired outside of authorized food supply distribution channels," according to the statement.

It's unclear what the substance was.

"We took immediate action to treat everyone involved with the best medical care available," said Maj. Gen. Sean C. Bernabe, senior mission commander of the 1st Armored Division and Fort Bliss. "Our leaders are engaged at every level to provide guidance, information, and care for their teammates."

Fort Bliss officials said in a statement they are cooperating with law enforcement officials, who are investigating.