The Mexican National Guard said Wednesday that two people had died in a gunfight with military police near a protest at a dam that diverts water away from an area hit by drought to the United States.

Mexican officials said farmers were upset over water from La Boquilla dam being transferred across the border of Chihuahua state and initially threw rocks and Molotov cocktails at officers Tuesday night.

The National Guard said officers were shot at when suspects allegedly possessing tear gas and gun ammunition were being arrested and taken in for processing.

The statement said the National Guard “repelled the aggression” and one person died at the scene and a second person died at the hospital.

During a news conference Wednesday, Mexican President Andres Manuel Lopez Obrador called in the incident “regrettable,” saying he would ask the Attorney General's Office to investigate the case.

Farmer Irma Gandara said the water transfer will create a significant economic problem for the state.

Gandara said they are not going to allow the biggest dam in Chihuahua, Boquilla, to be emptied.

The protest comes amid plans to divert more to the United States due to a “water debt” Mexico has accrued under a 1944 water-sharing treaty between the countries.

Lopez Obrador also said, he is asking the attorney general to investigate his country’s responsibilities but warned that Mexico could face sanctions if it did not divert water, after accumulating a deficit by receiving more water than it has provided.