The foreign minister of the tiny South American nation of Guyana has said that neighbouring Venezuela is “on the wrong side of history” as it risks sparking conflict over an oil-rich and long-contested swath of rainforest.

Tensions between the two countries have reached unprecedented heights ahead of a referendum on Sunday intended to rubber-stamp Venezuela’s claim on the region of Essequibo.

Among the five questions President Nicolás Maduro is asking his citizens is whether they should convert the 160,000 sq km area into a new Venezuelan state.

It remains unclear what the legal or practical implications of a yes vote would be, and the referendum is widely seen as a way for the deeply unpopular dictator to drum up public support ahead of presidential elections next year. But there are growing concerns that Maduro could push the country into war as he uses the century-old dispute to whip up patriotic fervour.

“People in the border region are very concerned,” Guyana’s foreign minister, Hugh Todd, told the Guardian. “Maduro is a despotic leader, and despotic leaders are very hard to predict.”