The United States on Thursday denied Venezuelan President Nicolas Maduro's claim that Washington is building secret military bases in Essequibo, an oil-rich region of Guyana that Caracas claims as its territory.

"There's no plans for a secret military base," White House National Security Council spokesman John Kirby said.

He urged both sides to abide by an 1899 court ruling on the border "and to do it peacefully," he added.

Maduro on Wednesday alleged secret US military bases in Essequibo, calling them an "aggression" and saying they were built "to prepare for an escalation against Venezuela."

Maduro's provocative remarks came as parliament held a ceremony commemorating a recent law laying out the defense of Guyana Essequibo, four months after a controversial, non-binding referendum overwhelmingly approved the creation of a Venezuelan province in the disputed region, sparking fears of a military conflict.

Guyana's foreign ministry called Venezuela's move to claim Essequibo an "egregious violation of the most fundamental principles of international law."

The dispute over Essequibo -- which makes up about two-thirds of Guyana's territory and has been administered by Guyana for more than a century -- intensified in 2015 after the discovery of oil deposits by US-based energy giant ExxonMobil.

Tensions soared after December's referendum. Days later, US forces held joint US-Guyana military exercises.

Both countries pledged last year not to use force to settle the border dispute, which is currently before the International Court of Justice in The Hague.