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Mexican military officials are apologizing for firing from a chopper at two U.S. Border Patrol agents early Thursday, but one lawmaker says the incident draws a disturbing contrast with the case of Andrew Tahmooressi, the U.S. Marine sergeant whose apology for accidentally crossing the border hasn't spared him a legal nightmare.

Mexican authorities were conducting a drug interdiction operation on the Tohono O’odham Indian Nation, which straddles the border, when they strayed into U.S. air space and fired at the agents, who were not injured. The reservation is a hotbed for drug smuggling, and authorities from both governments have conducted operations on it.

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"Early [Thursday] morning, a Mexican law enforcement helicopter crossed approximately 100 yards north into Arizona nearly eight miles southwest of the Village of San Miguel on the Tohono O'odham Indian Nation while on a drug interdiction operation near the border," U.S. Customs and Border Patrol spokesman Michael Friel said. "Two shots were fired from the helicopter but no injuries or damage to U.S. property were reported. The incident is currently under investigation."

Art del Cueto, president of the Border Patrol union's Tucson local, said Mexican officials contacted U.S. authorities to apologize for the incident.

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    While no one is claiming the incident was intentional, it brought to mind for some another accidental border crossing. Tahmooressi was arrested at the Tijuana Port of Entry March 31 after mistakenly crossing into Mexico, where he immediately told officials he had three registered guns in his pickup truck. But instead of letting him turn around, Mexican security officials charged him with possession of weapons and ammunition. He faces up to 10 years in prison if he is convicted.

    "It's ironic that Mexico says it acted accidentally in this case, and they ask we accept an apology, when they refuse to acknowledge an authentic mistake on Andrew's part," said Rep. Duncan Hunter, R-Calif., a former Marine who has championed Tahmooressi's cause. "There are mistakes and there are excuses. Andrew's actions were the result of wrong turn, a simple mistake. Mexico is just making an excuse and no different than the border incursion that are too regular, U.S. officials should approach this incident with absolute seriousness."

    Shawn Moran, a Border Patrol agent and vice president of the Border Patrol Council, said mistakes that put his colleagues in peril are not easily dismissed.

    "This is not the first incident where Mexican military/law enforcement has crossed the border and fired at our agents," Moran said. "It is a legitimate concern of ours and makes us wonder who we can trust on the south side."

    Fox News' Catherine Herridge contributed to this report