GEORGETOWN (Reuters) - A protester was shot dead as demonstrators took to the streets in Guyana on Saturday after opposition leaders and international observers accused the government of David Granger of rigging this week’s presidential election.

FILE PHOTO: Guyana President David Arthur Granger addresses the 72nd United Nations General Assembly at U.N. Headquarters in New York, U.S., September 20, 2017. REUTERS/Eduardo Munoz

Diplomats and foreign observers described credible evidence of fraud in the tallying of the results of Monday’s vote, which took place as the poor former British colony ramps up oil production in hopes of transforming its economy.

The unrest threatens to inflame decades of racial tensions between black Guyanese, who broadly support Granger’s APNU-AFC coalition, and Indo-Guyanese, who largely backed Irfaan Ali of opposition party PPP.

Across the South American country, PPP supporters blocked roads, burned tires and clashed with police.

Police said in a statement early on Saturday that they came under attack in the rural West Coast Berbice region after they cleared barricades set up on a road in an Indo-Guyanese community, adding that officers had killed an unemployed 18-year-old in response to the attack.

“Police ranks whilst performing duty on the Cotton Tree Public Road, West Coast Berbice, came under attack by protesters which resulted in several ranks being hospitalized and their attacker dead,” the statement said.

Berbice was for decades a sugar-producing region where mills were shut during Granger’s government, fueling anger among residents and leading the PPP to promise they would be reopened.

Police surrounded an elections commission office on Friday following accusations that the results of the vote in the country’s most-populous electoral district had been altered to favor Granger.

The country’s top court was expected on Saturday to rule on whether or not to block the elections commission from declaring Granger a winner.

The PPP filed an injunction on Friday to block a winner from being declared, on the grounds that the results in an area known as Region Four, the most-populous electoral district, had not been properly tabulated.

The elections commission did not respond to requests for comment. Granger’s office says he has done nothing illegal and cannot interfere in the process.

Guyana this year begins receiving hundreds of millions of dollars from oil being produced in fields off its coast by companies including Exxon Mobil Corp, creating a huge windfall for a population of less than 800,000.

That has raised the stakes of the country’s ethnically divided politics, with Indo-Guyanese and Afro-Guyanese both keen to control oil revenue so they can channel it toward their own constituencies.

Granger’s APNU-AFC coalition is largely made up of black Guyanese descended from African slaves while the PPP mostly represents descendants of Indian laborers who arrived in the 19th century to work on sugar plantations.