GEORGETOWN (Reuters) - The Organization of American States (OAS) on Friday withdrew its observer mission from Guyana’s disputed presidential election, citing concerns over the fairness and transparency of vote counting.

Top diplomats from the United States, European Union, Britain and Canada also walked out of the elections headquarters Friday in Georgetown, Guyana’s capital, where the count was being held.

The March 2 election has been marred by accusations of fraud in favor of President David Granger, who is running against Irfaan Ali of the opposition People’s Progressive Party to lead the former British colony.

Guyana’s Chief Justice Roxane George had blocked the electoral commission from declaring a winner in the vote and ruled on Wednesday that the country’s largest electoral district, known as Region Four, must resume counting votes with independent observers.

The OAS said the head election official in Region Four concealed official poll results from each voting site against court instructions, giving “credence to allegations that the numbers being tabulated do not correspond with the numbers on the statements of poll.”

Results from Region Four and thus the election as a whole “will not be credible and a president sworn in on the basis of those results will not be considered legitimate,” the diplomats from the United States, EU, Canada and Britain said.

The diplomats also cited concerns about “intimidation tactics” used against officials who championed a clean count.

The OAS said the opposition’s vote count was “vastly different” than those reported by the Region Four election head.

The dispute in which both parties claim victory led to violent demonstrations last weekend in which one protester was shot dead.

The vote will decide who is in power during the early years of an oil boom set to transform the economy of the poor country, which is beset by tensions between black Guyanese and Indo-Guyanese.