With the American president publicly stating he would be “OK” with attacks on Mexico to destroy drug cartels, diplomatic alarm bells began to ring when warning signs allegedly placed by the U.S. Department of Defense appeared on Mexican sovereign soil south of Matamoros.

Mexican naval forces removed the six signs Monday that claimed U.S. Department of Defense ownership over a portion of Playa Bagdad. The beach is a coastal area in Tamaulipas near the Río Grande, an environmentally sensitive region also known to be frequently controlled by cartels that are alleged to use the spot for the transshipment of narcotics.

Environmentalists raised alarms over the installation of the warning signs after a group claimed to have witnessed what appeared to be soldiers arriving from the United States.

According to Conibio Global, a local environmental organization, a field technician saw several men cross the river from the U.S. by boat and plant metal stakes bearing bilingual “Restricted Area” warnings. The signs stated that the land had been declared restricted “by authority of the commander” under a directive from the U.S. Secretary of Defense and referenced U.S. internal security law.