Two American soldiers were disarmed and questioned by Mexican troops wielding assault rifles this month while conducting a surveillance mission on US territory near the southern border, defense officials told CNN.

"On April 13, 2019, at approximately 2 p.m. CDT, five to six Mexican military personnel questioned two U.S. Army soldiers who were conducting border support operations in an unmarked (Customs and Border Protection) vehicle near the southwest border in the vicinity of Clint, Texas," US Northern Command told CNN in a statement.

"An inquiry by (Customs and Border Patrol) and (the Department of Defense) revealed that the Mexican military members believed that the US Army soldiers were south of the border," the statement added.

US officials confirmed that Mexican troops were armed with FX-05 Xiuhcoatl assault rifles. They surrounded the vehicle and disarmed one of the Americans. According to CNN sources, both Americans surrendered "in an attempt to de-escalate a potentially volatile situation."

"Throughout the incident, the U.S. soldiers followed all established procedures and protocols," the statement read.

"After a brief discussion between the soldiers from the two nations, the Mexican military members departed the area. The U.S. soldiers immediately contacted CBP, who responded quickly," Deputy Director of public affairs for NORAD and U.S. Northern Command John Cornelio told Newsweek.

Both US soldiers reported hearing someone yell vámonos in Spanish from the Mexican side. The Americans said, the Mexican soldiers went back to their "dark blue Ford pickup truck with a tactical rack in the back." The truck departed from the area, heading westbound on the border.