UNITED NATIONS (AP) — The U.N. Security Council scheduled an emergency closed meeting Friday at the request of Guyana following Venezuela’s weekend referendum claiming the vast oil- and mineral-rich Essequibo region that makes up a large part of its neighbor.

In a letter to the council president, Guyana’s foreign minister, Hugh Hilton Todd, accused Venezuela of violating the U.N. Charter by attempting to take its territory.

The letter recounted the arbitration between then-British Guiana and Venezuela in 1899 and the formal demarcation of their border in a 1905 agreement. For over 60 years, he said, Venezuela accepted the boundary, but in 1962 it challenged the 1899 arbitration that set the border.

The diplomatic fight over the Essequibo region has flared since then, but it intensified in 2015 after ExxonMobil announced it had found vast amounts of oil off its coast.

The dispute escalated as Venezuelan President Nicolas Maduro held a referendum Sunday in which Venezuelans approved his claim of sovereignty over Essequibo. Maduro has since ordered Venezuela’s state-owned companies to immediately begin exploration in the disputed region.

The 61,600-square-mile (159,500-square-kilometer) area accounts for two-thirds of Guyana. But Venezuela, which has the world’s largest proven oil reserves, has always considered Essequibo as its own because the region was within its boundaries during the Spanish colonial period.

In an Associated Press interview Wednesday, Guyanan President Irfaan Ali accused Venezuela of defying a ruling last week by the International Court of Justice in the Netherlands. It ordered Venezuela not to take any action until the court rules on the countries’ competing claims, a process expected to take years.

Venezuela’s government condemned Ali’s statement, accusing Guyana of acting irresponsibly and alleging it has given the U.S. military’s Southern Command a green light to enter Essequibo.

Venezuela called on Guyana to resume dialogue and leave aside its “erratic, threatening and risky conduct.”

In his letter to the Security Council, Guyana’s foreign minister said Maduro’s actions Tuesday ordering immediate exploration and exploitation of the oil, gas and mines in Essequibo “are flagrant violations of the court’s order, which is legally binding on the parties.”

Under Article 94 of the U.N. Charter, Todd said, if any party to a case fails to perform its required obligations, the other party — in this case Guyana — may take the issue to the Security Council.

“Venezuela is now guilty of breaching all these obligations, and the actions it has announced that it will soon take will only further aggravate the situation,” Todd said. “Its conduct plainly constitutes a direct threat to Guyana’s peace and security, and more broadly threatens the peace and security of the entire region.”

He asked the Security Council at Friday’s meeting to determine whether the situation “is likely to endanger the maintenance of international peace and security.”