The Coast Guard said it was investigating the incident alongside federal partners. It is unclear who fired the initial shots.
"No injuries to Coast Guard or other personnel were reported, and no damage to Coast Guard assets or equipment was reported," the Coast Guard said.
U.S. Ambassador to Mexico Ronald Johnson said the embassy "is helping to coordinate with Mexican forces that are being deployed in the border area where shots were fired against elements of the United States Coast Guard."
"Mexican military commanders will communicate directly with the U.S. forces deployed. Together, we intend to patrol both sides of our shared border, protect our communities, and disrupt the operations of criminal and terrorist organizations. Any threat from criminal or terrorist elements on either side of the border will be addressed swiftly," he added.
The Coast Guard launched Operation River Wall in October 2025, deploying additional personnel, boats and other assets to patrol the river between the U.S. and Mexico. The Coast Guard said its forces would focus on approximately 260 miles of the Rio Grande along the U.S.-Mexico border.
It was working closely with Border Patrol, the Pentagon and the Texas Military Department "to secure the border, disrupt illicit activity and protect the American people," the Coast Guard said, according to Stars and Stripes.
"We will continue to leverage a layered, integrated approach to control, secure and defend the border that strengthens our collective ability to counter illicit activity and safeguard our personnel and the communities we serve," the Coast Guard said.
The U.S. military said on Friday it had deployed hundreds of troops and their equipment to the Rio Grande Valley as part of planned preparations to address "historically observed seasonal increases in attempted illegal activity."
"The Sept. 26 Coast Guard encounter is an example of this uptick in illegal activity," the Joint Task Force-Southern Border said in a statement.