MEXICO CITY (AP) — A dispute over water payments to the United States widened in Mexico Wednesday, after President Andrés Manuel Lopez Obrador said Mexico has to pay its debts but angry farmers pushed back National Guard troops guarding a dam.

Under a 1944 treaty, Mexico and the United States are supposed to allow cross-border flows of water to each other, but Mexico has fallen badly behind and now has to quickly catch up on payments.

But the government of the border state of Chihuahua said Mexico should give the water to local farmers and hope that heavy summer rains will fill dams enough to repay the United States. Mexico has long used that wait-and-hope strategy, but it has led to problems in the past.

Mexico’s federal government dispatched National Guard officers to protect the La Boquilla dam Tuesday, but hundreds of farmers pushed and shoved them back hundreds of yards in a failed bid to take over the dam’s control room.

Earlier this week farmers took over a first dam near the border town of Ojinaga. The National Water Commission said they broke open locks and could put the downstream population in danger if they tried to open flood gates at the dam.

Both dams are located near the Texas border, west of the Big Bend area.

López Obrador stepped into the conflict Wednesday, saying there was enough water both for local farmers and payments to the United States.

“We do not want an international conflict,” the president said. “Treaties have to be lived up to. If we have signed a treaty, we have to comply with it.”

He accused some groups of trying to inject politics into the issue, and said some were asking for payments to farmers in exchange for the water. López Obrador replied with “what flavor do you want your ice cream,” a phrase used in Mexico to suggest someone is asking for too much.

Chihuahua Gov. Javier Corral said there wasn’t enough water for both local farmers and repayments. He said he would demand an explanation from the National Guard for its confrontation with the farmers, and said he would defend local farmers.

“We have never questioned that we have to fulfill our commitment to the United States … but first we have to ensure access to water for farmers in our state and then comply with the treaty,” Corral said.

According to the International Boundary and Water Commission, which oversees treaty compliance, Mexico has an obligation to give the United States about 1.75 million acre-feet (enough to flood a field with a foot of water) every five years (2.1 billion cubic meters). The United States, in return, gives Mexico even more water from other water sources further west.

In the current five-year cycle, Mexico kept up with payments between 2015 and 2017. But since Lopéz Obrador took office in December 2018, Mexico has delivered less water than it was supposed to. Mexico is still about 478,000 acre-feet (590 million cubic meters) short of meeting its requirement and must deliver that amount by the time the five-year cycle ends in October.