(CNN) - A Border Patrol agent died Sunday morning from injuries he suffered while on patrol in southwest Texas, US Customs and Border Protection said.
Rogelio Martinez, 36, and his partner were responding to activity while on patrol in the Big Bend Sector, which runs along the US-Mexico border, and the partner reported they were both injured, the agency said. The agents were patrolling near Interstate 10, in the Van Horn station area of the sector.
Customs officials would not say what type of activity the agents were responding to.
Other agents responded, provided medical care and transported both to a local hospital. CBP was later told Martinez had died, and his partner remains hospitalized. It was not clear what injuries they suffered. A Customs and Border Protection spokesman said Martinez was not shot.
"On behalf of the quarter of a million front line officers and agents of DHS, my thoughts and prayers go out to the family and friends of Agent Martinez and to the agent who is in serious condition," acting Secretary of Homeland Security Elaine Duke said in the statement.
On Sunday night, President Trump tweeted about the incident, writing, "We will seek out and bring to justice those responsible. We will, and must, build the Wall."
A tweet from Texas Gov. Greg Abbott expressing his condolences described the incident as an "attack."
"Our prayers are with the families of this Border Patrol Agent who was killed & the other who was injured in this attack in Texas. Our resources must be increased to prevent these attacks in the future. #txlege #tcot"
Texas Sen. Ted Cruz also called the incident an "attack" in a statement.
"This is a stark reminder of the ongoing threat that an unsecure border poses to the safety of our communities and those charged with defending them. We are grateful for the courage and sacrifice of our border agents who have dedicated their lives to keeping us safe. I remain fully committed to working with the Border Patrol to provide them with all the resources they need to safeguard our nation," Cruz said.
Carlos Diaz, a spokesman for the CBP, would not describe the incident in any further detail, saying the FBI is investigating.
"The FBI is still actively investigating the incident and gathering the facts," FBI spokeswoman Jeanette Harper said.
The Border Patrol's Special Operations Group and agents from CBP's Air and Marine Operations were searching the area for potential suspects or witnesses, the agency said.
Martinez had been a border patrol agent since 2013, officials said.
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