More than 30 soldiers in the Mexican Army crossed the border into Texas in Humvees on Tuesday before being processed and allowed to return to Mexico.
According to Customs and Border Patrol spokesman Rick Pauza, the accidental invasion occurred when 33 soldiers in four Humvees started crossing a bridge across the Rio Grande at Donna, Texas, and then realized they couldn't turn their vehicles around without entering the U.S.
A local newspaper, the Monitor of McAllen, Texas, reported that the Mexicans were chasing a resident of South Texas when they drove onto the bridge.
Without addressing the reason for the crossing, Pauza confirmed to ABC News that the incident had occurred and called it "inadvertent."
"There are times when an incident such as this occurs," said Pauza. "CBP has established protocols in place to handle such incident and all personnel have been processed as per those protocols. They returned to Mexico without incident."
In a statement, Mexico's National Ministry of Defense also confirmed that the incident had occurred, calling it "involuntary," and said it had happened "due to the vehicle turnaround being on the American side." The statement did not say why the Humvees drove onto the bridge.
Donna, Texas is in the Rio Grande Valley, just east of McAllen. The Donna-Rio Bravo Bridge officially opened in December 2010, but will not be open to commercial traffic till 2013.