By David Mardiste

TALLINN (Reuters) - Estonian Prime Minister Taavi Roivas lost a parliamentary vote of no confidence vote on Wednesday after his junior coalition partners deserted him, possibly opening up the path for a traditionally pro-Russian party to gain power.

Roivas' leadership has been increasingly under pressure over administrative reform, economic and social policies and appointments of party members to the board of state-owner companies.

Estonia, with 1.3 million people, has been a stanch NATO member, critical of neighboring Russia's annexation of Crimea and strongly supporting maintaining economic sanctions against the Moscow.

Roivas said after the vote, which he lost 63-28, that recent weeks had shown his coalition partners were negotiating behind the back of his center-right Reform Party.

"They have been negotiating to form a different kind of coalition with different kinds of ideas," he told reporters.

The Social Democrat party has begun talks for a possible new coalition with the traditionally pro-Russia Centre Party, local media has said. The party courts Russian speakers in a country where they make up 25 percent of the population.

The ousting of the Centre Party's long-time chairman Edgar Savisaar, who was openly pro- Moscow, has led to the appointment of Rein Ratas as new party chairman - a more moderate figure who has been critical of Russian foreign policy.

The current government was formed in April 2015 with an uneasy alliance between Roivas' Reform Party, Social Democrats, and the conservative-nationalist Pro-Patria and Res Publica Union holding 59 seats in the 101-seat parliament.

On Monday, the Social Democrats and Pro-Patria and Res Publica Union called on the prime minister to resign, saying there was too little trust between the coalition partners and that they wanted the formation of a new majority government.

The main point of tension within the coalition has been over domestic rather than foreign policy.

Previously, most political parties said they would not form a government with the Centre Party while Savisaar was chairman of the Centre Party.

(Reporting by David Mardiste; writing by Alistair Scrutton; Editing by Niklas Pollard)