U.S. guards fired at intruders on U.S. military installations in Panama on two occasions this week, the Pentagon said Thursday.

Pentagon spokesman Dan Howard said there were no U.S. casualties in the two separate incidents. One took place around midnight Tuesday and the other about 8 p.m. Wednesday, he said.Howard said that in the first incident at the Rodman ammunition dump adjacent to a U.S. Naval station, one of three intruders inside the facility fired at a U.S. Army guard, who returned the fire.

The intruder fired again, and the guard called for help from a Marine quick reaction force, Howard said.

The guard reported the intruders wore berets and carried small arms, Howard said.

In the second incident Wednesday night at an observation post west of Howard Air Force Base, three U.S. Army guards spotted a group of about 30 intruders and fired at them, the spokesman said.

In Panama, a spokeswoman for the U.S. Southern Command, which coordinates the activities of some 13,000 U.S. troops in Panama, said there had been a shooting incident, but she would not elaborate when or where it had taken place.

Another spokesman for the Southern Command confirmed there had been an intrusion near Howard Air Base, across the Panama Canal from Panama City, Wednesday night.

Howard said the three Army guards at the observation post near Howard Air Force Base fired anti-personnel claymore mines as a diversion.

The intruders retreated, Howard said, and a U.S. Army reaction team was sent to the post to help.

"There were no U.S. casualties," the spokesman said.

After the Tuesday incident, Howard said a "security sweep was made of the area with negative results." He said the investigation continues.

On April 12, a Marine was accidently shot dead when he was caught in the cross fire of fellow Marine guards when an estimated 10 to 12 intruders invaded a fuel storage facility near Howard.

Later the same day, a Marine patrol returned fire from a location where they had seen an estimated 40 to 50 intruders at the same tank farm.

Howard initially said the intruders in the first case were believed to be members of Panama's Defense Force because they wore camouflaged uniforms similar to those worn by the force.

He later retreated from that statement to emphasize there has been no positive proof the intruders were from the PDF.