(Adds further comment from Enel)
BRATISLAVA Dec 19 Enel wants more cash and more time to build two new units at the Mochovce nuclear plant in Slovakia, the country's prime minister said, describing the Italian utility's demands as "unacceptable".
Prime Minister Robert Fico, in power since April, said the Italian company wanted an extra 800 million euros ($1.1 billion) and expected construction work to go on for another 22 months.
Mochovce, operated by Slovak power company Slovenske Elektrarne, was originally expected to start commercial operation of the first new reactor by the end of this year and the next one in 2013.
Enel has a 66 percent stake in Slovenske Elektrarne, while the government holds the remaining 34 percent.
In March Enel pushed back the start of the third Mochovce unit to the end of 2013, while the fourth unit was supposed to follow eight months later.
Fico said the government had instructed its representatives on the board of Slovenske Elektrarne to object to Enel's call for additional funds, adding the economy ministry would draft a study by mid-January on the completion of Mochovce.
"(The) Italian investor keeps asking for more money, there is a proposal to boost costs of completion of the third and fourth blocs by around 800 million euros, which is absolutely unacceptable," Fico told reporters after a government meeting.
Enel said: "Slovenske Elektrarne is fully covering the costs associated with the design modifications and improvements with its own sources, and will not request any additional money from the state budget."
The Milan-based utility cited the need to meet significant international safety measures brought in after the March 2011 Fukushima disaster in Japan as key reasons for the delay at Mochovce, with costs originally estimated at 2.8 billion euros.
"Given the complexity of the new upgraded design of the reactors in Mochovce, the necessity to reorganize industrial infrastructure and the results of the EU's stress tests, the project had to be rescheduled," it added in an emailed statement.
Slovenske Elektrarne already operates two units at Mochovce and another two at its Jaslovske Bohunice power plant, with a total 1,950 megawatts of installed capacity.
In January all four nuclear reactors in Slovakia passed so-called stress tests against potential severe accidents, earthquakes, floods and other extreme events.
The analysis followed the Fukushima disaster, which spurred the European Union to mandate safety tests of its 143 reactors.
($1 = 0.7568 euro) (Reporting by Martin Santa; Editing by Helen Massy-Beresford)