The long-running spat over the oil-rich Esequibo region, which is being heard by the International Court of Justice (ICJ), escalated over the weekend when voters in Venezuela rejected the ICJ's jurisdiction and backed the creation of a new Venezuelan state.

Guyana has questioned the vote's legitimacy, put its armed forces on high alert, and said Venezuelan President Nicolas Maduro is disregarding ICJ orders about taking no action to change the status quo in Esequibo.

"We absolutely stand by our unwavering support for Guyana's sovereignty," White House national security spokesperson John Kirby told reporters, adding Washington supported a peaceful resolution to the border dispute between Venezuela and Guyana.

The U.S. State Department earlier this week said it thinks the Venezuela-Guyana border dispute cannot be settled through a referendum.

The United States has also said it would conduct flight operations within Guyana that build on its routine engagement. The U.S. Southern Command, which provides security cooperation in Latin America, was scheduled to conduct flight operations with the Guyanese military within Guyana on Thursday, the U.S. embassy in Georgetown said.

U.S. Secretary of State Antony Blinken spoke with Guyanese President Irfaan Ali late on Wednesday, the State Department said earlier.

Analysts and sources in Caracas have said the referendum was a effort by Maduro to show strength and gauge his government's support ahead of the 2024 election, rather than representing a real likelihood of military action.

(Reporting by Steve Holland; Writing by Kanishka Singh in Washington; Editing by Daniel Wallis)

By Steve Holland and Kanishka Singh