AUSTIN, Texas -- Two American soldiers patrolling along the southern border in Texas were stopped and questioned by a group of Mexican troops who believed they had crossed into Mexico, a U.S. military spokesman said Monday.

The interaction occurred as the Americans were conducting mobile surveillance camera operations at about 2 p.m. April 13 near Clint, Texas, said Maj. Mark Lazane, spokesman for U.S. Northern Command.

The U.S. soldiers were approached and questioned by about five or six Mexican troops, he said. An inquiry by U.S. Customs and Border Protection and the Defense Department revealed the Mexican troops believed the U.S. soldiers has crossed the border into Mexico.

"However, the U.S. soldiers were appropriately in U.S. territory. Though they were south of the border fence, U.S. soldiers remained in U.S. territory, north of the actual border," Lazane said.

After a brief discussion between the soldiers, the Mexican troops left, and the U.S. soldiers contacted Border Patrol agents.

"Throughout the incident, the U.S. soldiers followed all established procedures and protocols," Lazane said.

Newsweek obtained a copy of the incident report filed by the soldiers, which offers more details into the brief interaction. The Mexican troops approached the U.S. soldiers with rifles pointed at them, and removed a service pistol from the hip of one soldier and tossed it into an unmarked U.S. Border Patrol vehicle. The private and sergeant involved in the incident were part of 1st Battalion, 37th Field Artillery Regiment, out of Joint Base Lewis-McChord in Washington state, Newsweek reported.

This is the first incident of this kind since active-duty U.S. troops deployed to the border in late October, Lazane said. The two soldiers are part of the roughly 1,200 service members conducting mobile surveillance camera operations, a mission that began earlier this year after acting Defense Secretary Pat Shanahan authorized it in January.

That surveillance mission has resulted in the nearly 4,200 arrests and more than 1,700 drug seizures, April Grant, a spokeswoman for Customs and Border Protection, said April 8.

In total, there are about 2,800 active-duty service members at the U.S.-Mexico border, Lazane said.

Defense Department officials confirmed the incident as they contemplate sending more troops to the border. Shanahan said Friday that he's already begun reviewing options in anticipation of greater need at the border because Border Patrol is corralling record numbers of migrant families from Central America seeking asylum.

Shanahan said he's working with the Joint Staff to find a way to "do more monitoring and detection for them."

The border mission is authorized to continue through September, which is the end of the 2019 fiscal year.