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.

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.

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,