In brief
The Mexican foreign ministry stated that the U.S.-Mexico border is fixed by the 1970 Boundary Treaty and cannot be changed by any U.S. state. In response to Texas’ claim over nine islands in the Rio Grande, Mexico reaffirmed that sovereignty is decided by the International Boundary and Water Commission and that neither side may alter the river’s normal flow. Mexico will monitor the area and continue dialogue through established mechanisms.
Mexico’s foreign ministry said on Friday that the border with the United States cannot be altered by a U.S. state government, stressing that the 1970 Mexico‑U.S. Boundary Treaty sets the limits between the two countries. The statement was issued after Texas’ state agency declared nine islands in the Rio Grande, known as the Rio Bravo in Mexico, to be Texas property.
According to the treaty, the international boundary in the river follows the center line of the normal channel. That line determines which side of the river each island belongs to, regardless of previous sovereignty. Mexico said the International Boundary and Water Commission, the joint commission established by the two nations, is the only body authorized to decide on each island’s side.
The ministry added that under the treaty neither side may build works that could alter or obstruct the normal flow of the river. "Mexico will closely monitor any actions in the area and will continue to uphold the treaty," the ministry said, emphasizing its commitment to dialogue through established mechanisms.
In short, the Mexican government has made clear that a U.S. state does not have the authority to unilaterally change the border, and that international law governs sovereignty over the islands in question. Mexico pledged to monitor the situation and enforce the treaty’s provisions against any unilateral changes to the river’s flow or the border itself.