SAN DIEGO -- A border patrol agent died Friday in the rough desert mountains east of San Diego while tracking a group of suspected illegal aliens, the agency said Saturday.

Eric Cabral, 31, a San Diego native, was separated from his partner, and officials lost radio contact with him Friday. He was found on the ground and passed out near the De Anza Springs Resort near Jacumba and flown by Mercy Air to a local hospital.

Cabral was pronounced dead at 6:40 p.m. Cause of death has not been determined, but the case is not being treated as a homicide investigation, according to the county medical examiner's office.

Cabral joined the agency on Sept. 26, 2005, officials said.

"Agent Cabral lost his life serving and protecting the nation, and on behalf of the Border Patrol, we send our sincerest thoughts and prayers to his family during this difficult period," said San Diego Sector Chief Patrol Agent Michael Fisher.

Information regarding the memorial service will be provided later, officials said.