The State Department said it was the first time that the United States has rejected a request by Mexico for special delivery of water, which would have gone to the border city of Tijuana.

"Mexico's continued shortfalls in its water deliveries under the 1944 water-sharing treaty are decimating American agriculture-- particularly farmers in the Rio Grande valley," the State Department's bureau handling Latin America said in a post on X.

The 1944 treaty, which governs water allocation from the Rio Grande and Colorado rivers, has come under growing strain in recent years due to the pressures of climate change and the burgeoning populations and agriculture in parched areas.

The treaty sets five-year cycles for water deliveries by Mexico, with the latest set to end in October 2025.

US farmers and lawmakers complain that their southern neighbor has waited until the end of each cycle and has been coming up short in the latest period, as Mexico struggles with drought, while the United States has sent its share of water regularly.

A year ago, the last sugar mill in southern Texas shut down, with operators blaming a lack of water deliveries from Mexico.

After 18 months of negotiations, the United States and Mexico reached an agreement in November, days after Trump's election, to improve deliveries.

Hailed by the then administration of Joe Biden, the understanding calls for Mexico to work with the United States to deliver water in a more timely way, including earlier in each five-year cycle.

Mexican President Claudia Sheinbaum said Thursday before the State Department announcement that the water issue was "being dealt with" through the two countries' boundary and water commission.

"There's been less water. That's part of the problem," she told reporters.

- Water worries on both sides -

Tijuana, a sprawling city on the border with the US state of California that has become a hub for manufacturing, depends on the Colorado River for about 90 percent of its water and has suffered waste from creaky infrastructure.

The Colorado River, also a major water source for Los Angeles and Las Vegas, has seen its water levels shrink due to drought and heavy agricultural consumption in the southwestern United States, with around half of its water going to raise beef and dairy cattle.

In southern Texas, farmers have voiced fear for the future of cotton, citrus and other farming products without more regular water deliveries from across the border in Mexico.

US Agriculture Secretary Brooke Rollins on Wednesday announced $280 million in relief funds for Rio Grande Valley farmers.

"Texas farmers are in crisis because of Mexico's noncompliance," Senator Ted Cruz of Texas wrote on X, praising the State Department's water decision.

"I will work with the Trump administration to pressure Mexico into complying and to get water to Texas farmers."

The water dispute comes as Trump takes a tough approach to Latin American nations, especially on migration.

Trump has vowed to end arrivals of undocumented migrants, who largely come from Central America and Venezuela but transit through Mexico.

Trump deployed troops to the border and announced painful tariffs on Mexico, although he has since put them on hold until April 2.