Two U.S. troops were killed Tuesday in a vehicle rollover in New Mexico and another U.S. service member was hospitalized in serious condition, U.S. defense officials said, marking the first known military fatalities associated with President Donald Trump’s expanded mission at the southern border. The accident occurred at 8:50 a.m. near Santa Teresa, a border town west of El Paso, the military said in a statement. Three defense officials, speaking on the condition of anonymity because the matter is under investigation, said the incident involved U.S. Marines from Camp Pendleton in California. It was not clear what kind of vehicle they were operating.

Sean Parnell, a spokesman for Defense Secretary Pete Hegseth, could not be reached for comment. Neither could authorities in Doña Ana County.

Joint Task Force Southern Border, which oversees the military’s border mission from Fort Huachuca in Arizona, said in its statement that the identities of the deceased service members were being withheld until their families were notified.

The accident occurred as thousands of active-duty U.S. troops fan out from the Pacific Ocean to Texas as Trump seeks to seal the southern border to illegal crossings. While the Marines have primarily been concentrated in California, those involved Tuesday were assigned on a reconnaissance mission, as the Defense Department seeks to improve its understanding of the region, one of the defense officials said. The Trump administration has signaled it intends to give the U.S. military an even larger role at the southern border.

On Monday, Interior Secretary Doug Burgum traveled to New Mexico to transfer control of about 110,000 acres of federally controlled land to the Defense Department, allowing the U.S. military to take a more active role aiding law enforcement responsible for detaining illegal crossers. The plan to do so was first reported by The Washington Post last month and approved by Trump last week, effectively turning a 60-foot-wide strip of land along the border, known as the Roosevelt Reservation, into a satellite military installation.

Hegseth has enthusiastically embraced Trump’s focus on the U.S.-Mexico frontier, saying that after years of combat deployments overseas, it is time for the United States to protect its own boundaries. In February, he posted on social media that the administration is “dead serious about 100% OPERATIONAL CONTROL of the southern border.”