Guyana’s president has denounced an incursion by an armed Venezuelan naval vessel in disputed waters and home to a mammoth offshore oil deposit being developed by ExxonMobil.

A diplomatic spat is brewing after Venezuelan naval vessels entered ExxonMobil’s Stabroek block offshore Guyana, reportedly threatening its floating production, storage and offloading vessels operating there including the Prosperity FPSO amid an escalating territorial dispute between the two nations.

The South American neighbours are involved in a long-running dispute about which country owns the oil-rich Essequibo area Guyanese President Irfaan Ali said on Saturday that a Venezuelan naval vessel had entered his country's waters earlier in the day,

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.

Guyanese President Irfaan Ali said on Saturday that a Venezuelan coast guard patrol entered Guyanese waters earlier in the day, approaching an output vessel in an offshore oil block managed by Exxon Mobil .

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.