Playa Bagdad, Mexico - Men thought to be US troops landed on a beach in northeast Mexico on Monday and cordoned it off with signs declaring the area is considered "restricted" by the Department of Defense.

Fishermen in northeast Mexico reported that troops and military personnel from the US crossed the Rio Grande by boat and erected six signs declaring that the beach was a "restricted area."

The beach is part of Mexico's sovereign territory, and the US military has no jurisdiction over who can access it. Local authorities have confirmed that they did not grant the US government permission to install the signs.

"This Department of Defense property has been declared a restricted area," reads an image of one sign published online. "All persons and vehicles entering herein may be detained and searched."

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"Photographing or making notes, drawings, maps, or graphic representations of the area or its activities are prohibited unless specifically authorized."

Mexico's Foreign Affairs Ministry confirmed that the country's navy had removed the signs, but said they had no confirmation of whether the US military was responsible.

"Naval personnel located and removed six warning signs placed at Playa Bagdad, Tamaulipas as a preventive measure," the Foreign Affairs Ministry said in a statement translated from Spanish.

"The origin of the signs and their placement on national territory were unclear," it continued. "The Ministry of Foreign Affairs has contacted the US Embassy in Mexico about this incident."

The incident occurred shortly after President Donald Trump said he was "OK" with bombing Mexican territory in a stated bid to stop drug smuggling.

"It's not going to happen," Mexico's President Claudia Sheinbaum said in response to the threat. "We don't want interventions by any foreign government."