The incident occurred in Eagle Pass during an attempt to rescue migrants. Law enforcement sources initially told Fox News that the service member had drowned. However, the sources later said that the body that had been recovered was in fact a migrant, not the service member.
The Texas Military Department said in a statement that a soldier assigned to Operation Lone Star "has gone missing along a river during a mission-related incident."
"The Soldier has not been found," the statement said, calling reports of a fatality "inaccurate."
"The Texas Military Department, Texas DPS and Border Patrol are working rapidly to find the Soldier," the statement said.
The search is being treated as a drowning, and dive teams are still searching the water since the service member was not seen resurfacing from the river, sources told Fox News.
The Maverick County Sheriff later told Fox News that the soldier went missing in the water at around 8:30 a.m. local time while he was trying to save a female migrant. That migrant survived and is now in Border Patrol custody. However, the soldier still has not been located after more than six hours of searching.
Meanwhile, Rep. Tony Gonzales, R-Texas, tweeted out an image of the guardsman's armor, which reportedly he removed before jumping into the water.
"Please pray for the families of all those impacted," Gonzales tweeted.
Texas Gov. Greg Abbott's office said in a statement that it was continuing to work with the National Guard and other agencies as they search for the soldier, and said that updates would be provided as they become available.