UNITED NATIONS, United States, (AFP) – A top United Nations (UN) official on Monday urged authorities in the Dominican Republic to re-open its border with Haiti and use diplomacy to resolve a dispute over a shared river.

The Dominican Republic announced the border closure on Thursday in response to Haiti’s plans to build a canal on the Massacre River, arguing it violates several border treaties between the two nations, which share the island of Hispaniola.

William O’Neill, the UN’s top official on human rights in Haiti, said the border must be reopened.

“I urge the government to reconsider its decision which will have serious impacts on people on both sides of the border,” O’Neill said in Geneva.

He added that many businesses in the Dominican Republic depend on trade with Haiti and rely on Haitian workers.

The consequences of the border closure will be even direr for Haiti, which imports much of its food and medical supplies from its neighbor, according to O’Neill.

“Directors of medical clinics in Haiti have told me that they will not be able to care for their patients if access to the Dominican Republic is cut off,” said O’Neill. “Lives are at stake.”

Dominican President Luis Abinader reiterated Sunday that land, air and sea borders with Haiti will remain closed until the canal project is halted.

“The measures will be in force until we achieve the definitive stoppage of the canal under construction,” Abinader said in a televised address, referencing the closure of its “land, air and sea border” with Haiti, and the reinforcement of its military presence along its frontiers.

On Monday, his government called O’Neill’s statements “biased and unfortunate.”

The diplomatic crisis comes on top of existing tensions between the Caribbean neighbors over emigration from Haiti, one of the world’s poorest nations, to the richer Dominican Republic.

“The Republic of Haiti can make sovereign decisions on the exploitation of its natural resources,” the Haitian government said after the initial announcement of the border closure.

As part of the canal dispute, the Dominican government also suspended visas for Haitians. Ahead of the full border closure, it closed the Dajabon crossing — one of the most important, where a cross-frontier market takes place twice a week.

Dominican authorities are building a 160-kilometre (100-mile) concrete wall along the 380-kilometre border with Haiti to keep out undocumented migrants.