"A UH-72 Lakota helicopter assigned to the federal Southwest border support mission crashed... while conducting aviation operations near Rio Grande City, Texas," Joint Task Force North said in a statement.

"Two soldiers and one US Border Patrol agent were killed," it said, adding that a third soldier was injured.

"The cause of the accident is under investigation."

It occurred at around 2:50 pm (2150 GMT), according to JTF-N.

The aircraft went down in the town of La Grulla, Texas, located about 30 miles (48 kilometers) west of the city of McAllen, according to US media reports.