(CNN) -- A Mexican law enforcement helicopter crossed into Arizona and fired two shots near U.S. border agents in what Mexican authorities later acknowledged was a mistake, a U.S. law enforcement official said Friday.
No one was hurt in the incident, which happened at about 6 a.m. local time Thursday about 100 yards into U.S. territory as Mexican police were conducting an anti-drug operation, the official said on condition of anonymity.
Information about who authorities aboard the helicopter were targeting wasn't immediately available.
No one returned fire, and the helicopter returned to Mexico, the official said.
A separate official, U.S. border patrol spokeswoman Vivian McLoughlin, confirmed the helicopter crossed into U.S. territory, saying it happened at 5:45 a.m. Thursday. She did not provide further details.
Mexican authorities called U.S. authorities and acknowledged a mistake, saying shots were fired from the helicopter after it accidentally crossed the border, the first U.S. source said.