Bulgarian Prime Minister Boyko Borisov said Sunday he would ask members and supporters of his right-wing GERB party to vote "no" in a January 27 referendum on building a second nuclear power plant.

"We would give instructions to our party to vote on the referendum with 'No', 'No', 'No' and 'No!'," Borisov told TV7 television in an interview.

Instead he said he was in favour of building a new reactor at the country's existing plant and extending the operational capacity of the site's two reactors.

The referendum was initiated by the Socialist opposition after Borisov's government scrapped last March a deal with Russian state-owned company Atomstroyexport for a new 2,000-megawatt nuclear plant at Belene in the northwest.

Atomstroiexport's decision to sue Sofia for one billion euros ($1.3 billion) at the Paris-based International Court of Arbitration prompted the government to later hint that it might revive the project as a private investment.

Borisov had so far refrained from taking a clear stance on the referendum, which concerns Belene even if stopping short of mentioning the project by name.

This led environmentalists and the centrist and Socialist opposition to accuse him of using the referendum to reverse his previous decision and revive Belene without losing face.

Bulgaria currently has only two 1,000-megawatt reactors at its ageing Kozloduy plant, also in the northwest, after it was forced to shut four smaller units at the same plant to secure European Union accession in 2007. The two units are due to be decommissioned in 2017 and 2019.

Bulgarians are generally pro-nuclear, with 62.5 percent of the respondents in a recent poll of the state NCIOM institute backing its development, while 37.5 percent opposed.

Political analysts see the referendum as a way for both GERB and the Socialists to strengthen their voter bases ahead of the general elections in July.