A Mexican military helicopter flew into Texas airspace last weekend and that incident is under investigation, the U.S. Department of Defense said.
Several people noticed the chopper Sunday at an RV park near Zapata, about 100 miles northwest of the border city of McAllen, Zapata County Sheriff Sigifredo Gonzalez said.
"It looks to be military," Gonzalez said. "I don't know if it's being used to transport narcotics or people into the country."
U.S. Defense Department Maj. Tanya Bradsher said the flyover was under review.
"The incident did occur and it's still under investigation," she said.
The duty officer in the press relations office at Mexico's Defense Department, reached by telephone Friday, said she had no information on the reports.
Border Patrol spokesman Jason Darling said the Mexican military has been conducting operations nearby.
"Part of those operations encompass the area near Zapata along the Rio Grande. Some include helicopters," Darling said.
Witnesses also reported seeing a Mexican military helicopter over Texas on March 10, near Falcon Dam in Zapata County. The aircraft returned to Mexico without landing.