The United States issued a stern warning to the Nicolás Maduro regime on Saturday following reports that a Venezuelan patrol boat entered into Guyanaese waters, threatening ExxonMobil’s offshore operations.

Guyana and Venezuela have seen heightened tensions over control of the disputed Essequibo territory, a sprawling region rich in natural resources

Guyana’s government said Saturday that a Venezuelan naval patrol ship entered its waters and approached a vessel contracted by Exxon Mobil (NYSE:XOM) in the Straboek block, according to media reports.