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Mexican law enforcement on Thursday crossed into Arizona by helicopter and fired two shots at U.S. border agents, a union spokesman said.

The U.S. Border Patrol said in a statement that a Mexican law enforcement chopper crossed about 100 yards north into the Arizona desert. The helicopter then fired two shots on the Tohono O'Odham Indian Nation, which sits on the border. Shawn Moran, a spokesman for the border patrol union, said the Mexicans fired at agents but that none were hurt.

Sebastián Galván, a spokesman for the Mexican Consulate in Tucson, said the office was gathering information but did not have any details yet.

This incident was not the first one in which the Mexican military has veered across the international boundary.

In January, U.S. border agents confronted two heavily armed Mexican soldiers who crossed 50 yards inside Arizona, the Los Angeles Times reported. A standoff ensued, but nobody was hurt.

In 2011, more than 30 uniformed Mexican soldiers in military vehicles crossed the Rio Grande without authorization in an incident that was believed to be inadvertent.

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