The FBI is investigating a border patrol agent’s death as “potential assault” after he was attacked Saturday while on patrol in Texas, a bureau official said Tuesday afternoon.

Officials are still working to “gather the facts” of the incident, which left U.S. Customs and Border Protection Agent Rogelio Martinez dead and another agent, who has not been identified, injured.

U.S. Customs and Border Protection Agent Rogelio Martinez’s death is being investigated as a “potential assault,” an FBI official said Tuesday.  (REUTERS)

Martinez, 36, succumbed on Sunday to traumatic head injuries and a number of broken bones he sustained during the attack — which officials have said appeared to be an “ambush” — near the Texas border with Mexico.

The two were found in a culvert late Saturday near Van Horn, which is roughly 30 miles from the southern border.

A National Board Patrol Council (NBPC) official told Fox News that illegal immigrants appeared to have attacked the agents with blunt objects, possibly rocks.

“We don’t know exactly what happened because we weren’t there,” Brandon Judd, president of the NBPC, said. “However, just from agents that were working in the area, reports are saying it was an attack and it would appear to be an ambush.”

Judd added that “there were no indications the agents fired their weapons” and there were no signs of a stabbing, citing accounts he received from agents who responded to the incident.

BORDER PATROL AGENT APPEARED TO BE AMBUSHED BY ILLEGAL IMMIGRANTS, BASHED WITH ROCKS BEFORE DEATH

FBI Spokeswoman Jeanette Harper told the San Antonio Express-News on Sunday that Martinez and his partner were “not fired upon.”

While the FBI is investigating the attack on the officers as a “potential assault,” Special Agent in Charge Emmerson Buie Jr. said they’re currently treating the incident as an assault on a federal officer.

However, officials said they wouldn’t rule out the possibility that the agents were injured in another way.

Texas Gov. Greg Abbott has offered a reward of up to $20,000 “for information leading to the arrest and conviction of the person or persons responsible” for the attack. The FBI is also offering a reward of up to $25,000 for information.

Martinez had been an agent with the Border Patrol since 2013. He’s the second agent to have died this year.

The Border Patrol website lists 38 agents, not including Martinez, who have died since late 2003.

The Associated Press contributed to this report.

Nicole Darrah covers breaking news for FoxNews.com. Follow her on Twitter @nicoledarrah.

Read more: http://www.foxnews.com/