A helicopter carrying National Guard members and a Border Patrol agent crashed on Friday in southern Texas near the border with Mexico, killing three of its occupants and critically injuring the fourth, officials said.

The helicopter, which crashed at 2:50 p.m., was a UH-72 Lakota, Joint Task Force North said in a statement. Two of the dead were soldiers, and the third was a Border Patrol agent, it said.

The helicopter was patrolling the border and following people who were crossing into the United States illegally when it crashed in an open field, said Eloy Vera, the Starr County judge and the top local official in the county. He said he was notified of the crash about 7:30 p.m. by the county sheriff’s office, which later provided more details to him. There was no one on the ground where the helicopter crashed, Judge Vera said.

The sheriff’s office said in a statement that it was assisting with a helicopter crash in eastern Starr County that could involve four people.

Three of the people on board were men and one was a woman, Judge Vera said, adding that the Border Patrol agent had been stationed in Rio Grande City.

Joint Task Force North and Judge Vera said that they would not share the names of the victims because their families had not been notified.

The Department of Homeland Security, National Guard, Customs and Border Protection and Texas Department of Public Safety did not comment.

This is a developing story.

Emily Schmall contributed reporting.