Eleven soldiers were injured at Fort Bliss on Thursday after they “ingested an unknown substance” during a training exercise, a public affairs officer said in a press release. Investigators believe the mystery substance was antifreeze or something similar and that the soldiers drank it accidentally, an Army official told the Washington Post. All eleven are being monitored by medical staff, including two soldiers who are reported to be in critical condition. The substance was “acquired outside of authorized food supply distribution channels,” officials said.

“Medical professionals are working hard to attend to the injured and provide all available aid,” Fort Bliss Public Affairs said, according to CNN. The base is located in El Paso and is home to multiple organizations including the 1st Armored Division and the U.S. Army Sergeants Major Academy.