CARACAS, Venezuela, (AFP) — Venezuelans began voting Sunday in a referendum that the government hopes will strengthen its century-old claim to the oil-rich Essequibo territory controlled by neighbouring Guyana.

“Essequibo is ours!” say posters plastered on walls lining the streets in Caracas, part of an intensive campaign by the government of President Nicolas Maduro, who is seeking re-election next year.

“Today we are voting as Venezuela in just one colour, one feeling. Our vote is for Venezuela to be respected,” Maduro told reporters after he voted at a military base.

Voting started at 6 am (1000 GMT) and was to end at 6 pm (2200 GMT), with results expected in the early hours of Monday morning.

The Maduro government has said it is not seeking justification to invade or annex the territory, as some in Guyana, a former British colony, fear.

And regardless of the outcome of the vote by around 20 million eligible Venezuelans, little will change in the short term: The people of Essequibo are not voting, and the referendum is nonbinding.

But tensions have been rising since Guyana took bids in September for several offshore oil exploration blocks, and after a major new find was announced in October. Its petroleum reserves are similar to those of Kuwait, with the highest reserves per capita in the world.

Meanwhile, Maduro’s government has sharpened its rhetoric and conducted military exercises in the area.

And Brazil has strengthened its own troop presence near the border with Venezuela, saying it is concerned by the “climate of tension.”

Venezuela has claimed the huge territory for decades — even as its 160,000 square kilometres (62,000 square miles) represent more than two-thirds of Guyana, and its population of 125,000 is one-fifth Guyana’s total.

Caracas contends that the Essequibo River to the east of the region is the natural border between the two countries, as declared in 1777 under Spanish rule, and that Britain wrongly appropriated Venezuelan lands in the 19th century.

Guyana, however, asserts that the border was set in the British colonial era and was confirmed in 1899 by a court of arbitration. It says the International Court of Justice (ICJ), the UN’s top judicial body, has validated this finding.

Guyana has asked the ICJ to block the referendum, saying it amounts to a violation of international rights, but in vain.

On Friday, the ICJ called on Caracas to take no action that would modify the disputed lands — but it did not mention the referendum. And Caracas had vowed to go ahead regardless.

“We believe that justice, not force, should be the arbiter of international disputes,” Guyanese President Irfaan Ali said Friday from the United Arab Emirates, where he was attending the COP28 international climate summit.

Ali met there with British Foreign Minister David Cameron to discuss the controversy.

Maduro, for his part, lashed out at Ali on Friday, calling him “reckless (and) insolent” and suggesting he was working for US energy giant ExxonMobil.