Mexico's failure to keep up with its water deliveries has sparked a diplomatic spat with its largest trading partner.

Mexico plans to deliver water to farmers in drought-stricken Texas, a day after President Donald Trump threatened tariffs and sanctions for not providing water from the Rio Grande River under a 1944 treaty.

President Trump has threatened to slap new tariffs on Mexico for failing to deliver water under a decades-old treaty. But climate change has decimated river flows.