Sixty illegal immigrants employed as contract workers at industrial plants – including refineries, power plants and an air cargo facility – were arrested as possible threats to homeland security, officials announced Friday.

The suspects “had access to sensitive critical infrastructure locations and therefore pose a serious homeland security threat,” said Michael J. Garcia, assistant secretary for U.S. Immigration and Customs Enforcement. “Not only are their identities in question, but given their illegal status, these individuals are vulnerable to potential exploitation by terrorist and other criminal organizations.”

The arrests _ made Thursday and Friday in Texas, California, Louisiana, Mississippi, Oklahoma and Texas _ came as part of federal efforts to protect key facilities around the country.

The illegal immigrants were working at seven petrochemical refineries, three power plants, an air cargo facility and a pipeline facility. There is no evidence the individuals _ from Mexico, Guatemala and Honduras _ have terrorist ties.

The immigrants worked for Brock Enterprises, which supplies contract workers to facilities nationwide. Brock is not a target of the investigation and is cooperating, government officials said.

Brock spokesman John Thomasson declined to comment.

The workers were arrested on administrative immigration violations, but some could face federal criminal charges for re-entering the country after deportation or use of fraudulent documents to gain employment.

The arrests came after immigration officials found discrepancies in their review of employment records of some of Brock’s contract workers.