CALEXICO, Calif. -

U.S. and Mexican law enforcement agencies are investigating a couple of attacks on groups of illegal immigrants smuggled into the United States this month just south of the Coachella Valley.

Border Patrol agents say they arrested two groups of illegal immigrants that were assaulted and robbed at gunpoint on February 16 and 17 near Ocotillo, just west of Calexico.

The first group of five illegals were being smuggled through mountains west of the Calexico port of entry February 16 when they say they were robbed by two masked men armed with high-powered rifles.

The group said their assailants also assaulted them just before entering the United States. 

The Border Patrol says a second group of gunmen confronted the entire group a short time later and tried to rob them of their belongings when a gunfight broke out.

That battle allegedly left one gunman dead at the scene, although no body has been found.

The group of illegals then fled north into the U.S. where Border Patrol agents arrested them. 

A shotgun was later found at the crime scene with several used shotgun shells.

Mexican authorities are investigating.

"These unfortunate events highlight the inherent dangers of crossing the border illegally", said Chief Patrol Agent Carla L. Provost of the El Centro Sector. 

The second assault and robbery occurred in the same area February 17, when eight illegal immigrants say several gunmen confronted them while carrying high-powered rifles.

The immigrants say the gunmen held them hostage for several hours before they overpowered them in a fight that left two of the gunmen dead and one of the illegals shot in the face.

That second group of aliens called 911 for help. 

The injured victim was flown to Desert Regional Medical Center in Palm Springs. 

Authorities later found a ski mask at the crime scene during a week long operation in the area, also an AK-47, one Ruger .223, two large-capacity ammunition magazines and  two deceased Mexican nationals. 

Provost said, "Border violence is of great concern to the governments of Mexico and the United States and we will continue to cooperate and collaborate with our partners in an effort to establish a safe and secure border."