SAN DIEGO -- Four heavily armed Mexican soldiers were detained when they ventured into the United States and encountered a Border Patrol agent, authorities said Sunday.

The soldiers, dressed in camouflage fatigues, crossed the U.S-Mexico border Saturday night near Tecate, Mexico, while on a counterdrug mission, Border Patrol spokesman James Jacques said.

A Border Patrol agent tracking footprints found himself face to face with the soldiers, one of whom had unholstered his handgun. Each of the soldiers carried a handgun, three were carrying submachine guns and one had an M-16 rifle, Jacques said.

The Border Patrol agent unholstered his weapon and identified himself, he said. The Mexican soldiers identified themselves and, realizing they had entered U.S. territory, cooperated with the agent. They were taken to a nearby Border Patrol station.

After the soldiers' unit commander and the Mexican consulate verified their status, the soldiers were returned to Mexico through the San Ysidro Port of Entry.

"This could easily have escalated into a real tragedy," Jacques said. "Thankfully, cooler heads prevailed."