It was a sight that confused Elias Ibarra and his team.

On Monday morning, Ibarra said he and his team were at Playa Bagdad in Matamoros just south of the border across from Boca Chica Beach when they saw a group of people approaching by boat.

“A group of people without logos, ID's or a uniform took a fishing boat from the U.S. side of the border and docked south of the Rio Grande,” Ibarra said, adding that the unidentified men put up signs at the Mexican beach.

The signs said the property had been declared a “restricted area” by the Department of Defense, and unauthorized entry is prohibited.

Ibarra, an environmental activist, said he got in touch with the Mexican Federal Attorney for Environmental Protection. The Mexican Navy arrived later that day and removed six signs for being on Mexican territory. 

On Tuesday, Mexico's President Claudia Sheinbaum said that the International Boundary and Water Commission was getting involved.

The signs appear to be similar to those installed across the Texas-Mexico border as part of President Trump's executive order to restrict entry onto portions of the border.

The signs designate National Defense Areas, which are considered extensions of Joint Base San Antonio.

READ MORE: National Defense Area established in the Rio Grande Valley

Channel 5 News reached out to the Mexican consulate in Brownsville, Mexican foreign relations, SpaceX and the Department of Defense for comment.

A Pentagon official told Channel 5 News that U.S. military contractors placed signs marking the National Defense Areas at the mouth of the Rio Grande “as planned” to identify National Defense Area #3 within the South Texas National Defense Area.

The Pentagon official added that changes in water depth and topography altered the perception of the international boundary's location. Contractors will continue to mark the National Defense Area, and coordinate with appropriate agencies to avoid future confusion, the Pentagon official said.

During a Tuesday press conference, Sheinbaum said government agencies from the U.S. and Mexico have to clearly identify the boundary between both countries at Playa Bagdad near the Gulf.

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