VAN HORN, Texas (AP) - The FBI has taken over the investigation of the death of one U.S. Customs and Border Protection agent and the serious injury of another.

Border Protection spokesman Carlos Diaz confirmed to The Associated Press in an email that the FBI was in charge of the investigation.

Agent Rogelio Martinez and his partner were transported to a local hospital Sunday after sustaining injuries while on duty in the Big Bend area of Texas. Martinez died and his unidentified partner is in serious condition.

Spokesman Douglas Mosier says Martinez was 36 years old and from El Paso. He had been a Border Patrol agent since August, 2013.

No details of how they sustained injuries have been released.

Earlier Sunday, local authorities were searching Texas' Big Bend for potential suspects and witnesses after a Martinez was fatally injured responding to activity there.

Border Patrol records show that Big Bend 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 and the Rio Grande make it a difficult area for people to cross illegally into the U.S. from Mexico.