A helicopter flying over the US-Mexico border in Texas has crashed, killing two national guard soldiers and a border patrol agent, the US military has said.

Another soldier on board was injured.

The UH-72 Lakota helicopter was assigned to the federal government’s border security mission when it went down near Rio Grande City on Friday, the joint taskforce north said. The cause was under investigation.

The crash happened mid-afternoon while the helicopter was conducting aviation operations, according to the taskforce’s statement.

Starr County judge Eloy Vera, the county’s top official, said those onboard included one woman and three men. He said the person who was injured was in critical condition

The names of those killed were not immediately released.

A US Border Patrol spokesperson did not immediately return messages seeking comment.

The Starr County sheriff’s office posted on Facebook on Friday that it was assisting with a “downed helicopter incident” on the east side of the county.

Vera said the scene had been secured by the sheriff’s office and that federal officials were on the way.

The border region is heavily patrolled by both state and federal authorities, including routine aerial surveillance.

In January, a Texas Department of Public Safety helicopter patrolling the state’s border with Mexico lost power and crashed, officials said at the time. The co-pilot suffered a minor hand injury and the helicopter was significantly damaged.

That helicopter was flying as part of Operation Lone Star, Texas governor Greg Abbott’s nearly $10bn border mission that has tested the federal government’s authority over immigration.