The US is holding military drills in Guyana following a referendum in Venezuela where voters overwhelmingly supported their country's claim to the oil-rich Essequibo region.
"In collaboration with the Guyana Defense Force, the US Southern Command will conduct flight operations within Guyana on December 7," the American embassy in Georgetown said in a statement Thursday.
The US plan prompted Brazilian President Luiz Inacio Lula da Silva to warn against a war in South America.
"If there's one thing we don't want here in South America it's war," the veteran leader told a summit of the Mercosur regional bloc in Rio de Janeiro.
The disputed region has been controlled by Guyana, a former British and Dutch colony, for more than a century, but Venezuela also claims sovereignty over it which comprises some two-thirds of Guyanese territory.
The 160,000 square km (61,776 square mile) territory around the Esequibo river has found significance in recent years, after the discovery of offshore oil and gas by US energy company ExxonMobil. The maritime border between the two countries is also in dispute.
Venezuela’s electoral authority said on Sunday that all questions passed with more than 95% approval and at least 10.5 million votes were cast for ‘yes’.
“Popular mandate is sacred,” President Nicolas Maduro said at an event on Monday. “That is the path with which, as head of state, I’ll take all my actions and all our actions from here forward.”
“A new era in the fight for our Guayana Esequiba has begun,” he added, using the proposed name for the new Venezuelan state. “Now we will recover Venezuela’s historical rights.”
Caracas claims the Essequibo River to the region's east forms a natural border recognized as far back as 1777.
Essequibo is home to 125,000 of Guyana's 800,000 citizens.
The UN Security Council will meet behind closed doors on Friday to discuss the heightened tensions, as the International Court of Justice (ICJ) in The Hague is expected to determine where the region’s borders should lie.