PHOENIX (REUTERS) - US authorities are investigating two shots that were fired from a Mexican helicopter when it crossed the border into Arizona, although no injuries or damage to U.S. property were reported, the US Border Patrol said on Friday.

The US Customs and Border Protection, in a statement, said the incident took place early on Thursday at the Tohono O'odham Indian Nation reservation in southern Arizona. "A Mexican law enforcement helicopter crossed approximately 100 yards north into Arizona nearly eight miles southwest of the Village of San Miguel," US border officials in Tucson said. "The incident is currently under investigation," they added.

A spokesman for Mexico's federal prosecutor said the incident had "apparently involved an army helicopter," but declined to elaborate. Mexican army officials could not immediately be reached for comment.

The US southern border has often been the scene of law enforcement operations to counter drug trafficking gangs and illegal immigrant smugglers.