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BRATISLAVA, March 28 (Reuters) - Shareholders of Slovakia's biggest power utility approved a higher cost estimate for a long-delayed nuclear power plant but could not agree on how to finance the extra 800 million euros, company and government officials said on Wednesday. The new price tag for the two new 470-megawatt units at Mochovce is 5.4 billion euros ($5.8 billion), a Slovenske Elektrarne spokesman said on Wednesday, double the original plan.
Slovenske is owned by the government, with a 34 percent stake, and a joint venture between Italy's Enel and privately-held Czech energy group EPH.
Under a shareholders' agreement, Enel is in charge of the plant's completion, and the government blocked a proposal to raise the firm's equity, Economy Minister Peter Ziga said.
Ziga said the government agreed to the cost increase on condition that the majority shareholder -- the Slovak Power Holding owned equally by Enel and EPH -- will secure the additional 800 million euros.
"We refused to raise the company's capital, it's up to the majority shareholder to provide financing," Ziga said.
"One option would be a shareholder loan. It is questionable whether there's economic room for a commercial loan," he added.
There have been lawsuits between the Italian firm, which bought a 66 percent stake in the power utility in 2006, and the centre-left government of Prime Minister Robert Fico, a supporter of greater state control over strategic industries.
According to a 2015 deal, Enel will gradually sell its 66 percent stake to EPH. Fico has repeatedly demanded Enel should not pull out completely until Mochovce is completed.
But Enel said Mochovce's expansion was a Slovenske Elektrarne project and a responsibility of all shareholders.
"According to the signed agreement, Enel is not responsible for the funding of the project, Slovenske Elektrarne is in charge of the project completion and its funding," the company said in a statement.
"Slovenske Elektrarne is currently working on the options for financing the project completion. Discussions are ongoing to identify a solution to the financing needs of the company and information will be provided at the appropriate time," it added.
The construction of two new units at Mochovce, which already operates two reactors, has been beset by delays and budget overruns.
Reuters reported last October the cost would jump to 5.4 billion euros. The estimate had already risen to 4.6 billion euros from an initial 2.8 billion euros.
The plant's launch is now envisaged in November 2018 for the first reactor and November 2019 for the second, a year behind the previous schedule, Slovenske's spokesman said. ($1 = 0.9266 euros) (Reporting by Tatiana Jancarikova; editing by Susan Thomas/Ruth Pitchford)