Authorities were scouring West Texas on Monday for those behind an apparent attack that killed one U.S. border agent and injured another.

U.S. Customs and Border Protection issued a statement Sunday that was thin on details about what happened, saying the two agents “were responding to activity” while on patrol near Interstate 10 in the area of Van Horn, which is about 30 miles (48 kilometers) from the border with Mexico and about 110 miles (175 kilometers) southeast of El Paso.

CBP spokesman Douglas Mosier said 36-year-old agent Rogelio Martinez and his partner were transported to a hospital, where Martinez died. Martinez’s partner, whose name hasn’t been released, is in serious condition.

Elected officials referred to it as an attack, with Gov. Greg Abbott tweeting that “resources must be increased to prevent these attacks in the future.” And Republican Sen. Ted Cruz also referred to it as such, saying in a news release: “We are grateful for the courage and sacrifice of our border agents who have dedicated their lives to keeping us safe.”

At a Cabinet meeting Monday, President Donald Trump offered his condolences to Martinez’s family and said the wall he has promised to build along the border between the U.S. and Mexico is on the agenda.

Trump said the injured agent was “brutally beaten and badly, badly hurt” but “looks like he’ll make it.”

Authorities haven’t said whether they have any suspects or whether they think smugglers or people who were in the country illegally were involved.

Kevin McAleenan, acting commissioner of CBP, said in a letter sent to border agents that Martinez was unconscious when agents found him, with “multiple injuries” to his head and body.

Jeanette Harper, FBI spokeswoman for the El Paso field office, told the San Antonio Express-News only that Martinez and his partner were “not fired upon.” The FBI has taken over the investigation.

Border Patrol records show that the agency’s Big Bend sector, which includes the area where Sunday’s attack took place, accounted for about 1 percent of the more than 61,000 apprehensions its agents made along the Southwest border between October 2016 and May 2017. The region’s mountains make it a difficult area for people to cross illegally into the U.S. from Mexico.

The Border Patrol website lists 38 agents, not including Martinez, who have died since late 2003 — some attacked while working along the border and others killed in traffic accidents. Martinez is the second agent to have died this year.

(AP)