- WASHINGTON - Rep. Tom Tancredo, R-Colo., accused the Mexican army Tuesday of staging a "military incursion" Friday night into southern Arizona that ended with Mexican soldiers firing shots at a U.S. Border Patrol vehicle.

Lori Haley, an Immigration and Naturalization spokeswoman, confirmed that an incident occurred in a remote area near Ajo, Ariz.

A U.S. agent spotted three Mexican soldiers in a Mexican Humvee on U.S. soil and was attempting to leave the area when the rear window of his vehicle was apparently shattered by gunfire, she said. The agent was leaving the area "in an effort to avoid a confrontation" with the Mexicans, she said.

"Because of the seriousness of the incident" Haley said, U.S. authorities launched a formal investigation and are asking Mexican authorities to do the same.

The Mexican government previously has rejected Tancredo's charges that Mexican police and military units frequently cross the border. Tancredo, who leads a group of lawmakers opposed to liberalizing immigration laws, has said U.S. officials believe the incursions are related to drug trafficking.

The Republican from Littleton said he fears gunplay between U.S. and Mexican authorities unless officials stop the incursions. "Unless we open our eyes and recognize that what's happening along the U.S.-Mexico border is real, one of our guys is going to get killed," he said.

The INS confirmed the incident, but Tancredo's version differed somewhat. He said 10 soldiers were involved and the shot damaged more than the Border Patrol's rear window. He also said the Mexicans came 10 miles into the U.S before they were spotted.

Tancredo said U.S. agents believe the shots were fired because Mexican authorities were pursuing drug dealers into the U.S.

"They are saying they had interdicted a huge shipment of drugs," he said. "Therefore everyone was antsy."

But "regardless of the circumstances, they had happy trigger fingers," he said.

The U.S. vehicle was "clearly marked" and should have been recognizable, he said.

The agent told him, " "As far as I am concerned, that (incursion) should be an act of war,' " Tancredo said.

On May 3, Tancredo wrote Mexican President Vicente Fox demanding that he halt "incursions" by Mexican law enforcement officers into the U.S.

Fox didn't respond.