By Felix Light

TBILISI (Reuters) -U.S. data and polling firm Edison Research said on Friday the differences between its exit poll of Georgia's parliamentary election and the official results pointed to "manipulation" of the vote, becoming the second such pollster to do so.

Georgia's electoral commission has said the ruling Georgian Dream party, seen as being controlled by billionaire founder Bidzina Ivanishvili, won with 54% of the vote, an outcome that opposition parties and the president denounced as fraudulent.

Opposition parties have called a protest on Monday against the election result.

In a statement, the U.S. company said, "The 13-point difference between Edison’s estimate and the official result of 54% for Georgian Dream cannot be explained by normal variation alone and suggests local-level manipulation of the vote."

It added: "Edison’s review found that the deviation from statistically expected results was widespread but most pronounced at specific polling locations in rural areas."

These sites were the most likely to have experienced significant vote manipulation, it added.

Georgian Dream underperformed in larger cities, but drew margins of up to 90% in some rural areas.

Georgian Dream and the election panel did not immediately comment on the pollsters' statements, but both have repeatedly said the election was free and fair.

Widely seen as pivotal for Georgia, the election offered a choice between further European integration under the pro-Western opposition, or closer ties with Moscow under a ruling party that critics say is increasingly authoritarian.

Edison's exit poll, commissioned by the pro-opposition television channel Formula, showed Georgia's four main opposition parties on course for a majority in the election.

On Thursday, HarrisX, another U.S. pollster that ran a separate exit poll for pro-opposition television channel Mtavari Arkhi, said the official results were "statistically impossible".

Opposition parties have repeatedly pointed to the two exit polls, which showed Georgian Dream attracting less than 45% of the vote, as evidence that the election was falsified.

A third exit poll by Georgian pollster GORBI, for the pro-government Imedi television station, showed Georgian Dream winning with 56%.

Observer groups, including the 57-nation Organisation for Security and Co-operation in Europe (OSCE), have said violations, such as ballot-stuffing, voter intimidation and bribery could have swayed the election, but have stopped short of saying it was outright stolen.

Western countries have called for an investigation into the violations, while Russia has accused them of interfering in Georgian affairs.

(Reporting by Felix Light; Editing by Tom Hogue and Clarence Fermamdez)