CARACAS, Venezuela, (AFP) – Venezuela on Tuesday lashed out at neighbouring Guyana for auctioning off oil blocks off the coast of a disputed region that Caracas claims as part of its territory.

Venezuela has long argued that the 160,000-square-kilometre (62,000-square-mile) region of Essequibo, administered by Guyana, should fall within its borders.

The historic row -- tiny Guyana is only 215,000 square kilometres in total -- intensified after the discovery of crude oil deposits off the region's coast in 2015.

A dispute over the 19th-century border is pending before the International Court of Justice (ICJ) in The Hague at Guyana’s request, and despite objections from Venezuela.

Venezuela "firmly rejects the illegal auction of oil blocks" by Guyana pending an ICJ decision, the foreign ministry in Caracas said in a statement.

"The government of Guyana does not have sovereign rights over these maritime areas," it added, claiming Georgetown was violating international law.

Guyana's presidency hit back, saying the government "reserves the right to pursue economic development activities in any portion of its sovereign territory."

A former Dutch and British colony, Guyana claims its border with Venezuela was fixed by an arbitration tribunal in 1899 after a crisis that led the United States to intervene on behalf of Caracas, which was close to Washington at the time, against the British.

In 2018, Guyana asked the International Court of Justice in The Hague to ratify the 1899 border.

But Venezuela says the Essequibo river to the east of the region forms a natural border between the two countries, recognized since 1777 until the arbitration ruling, which it rejects.

Essequibo is home to 125,000 of Guyana's 800,000 residents, according to a decade-old census.

The country boasts oil reserves of at least 10 billion barrels, more per capita than Brunei, Kuwait or the United Arab Emirates.