(Adds project background, higher costs, other details)
BRATISLAVA, Oct 19 (Reuters) - Slovakia's Nuclear Regulatory Authority said on Wednesday the expected completion of a third block at the Mochovce nuclear power plant had been delayed by a year to November 2017.
The fourth block should be finished a year later, in November 2018, the regulator added.
The Mochovce plant is run by the country's biggest electricity producer Slovenske Elektrarne, owned by Italy's Enel , Czech group EPH, and the Slovak state.
The project has faced several delays and cost overruns, partly due to increased security standards following Japan's Fukushima accident in 2011.
Economy Minister Peter Ziga said this month the costs were likely to run higher than the 4.6 billion euro ($5.1 billion) budget but he did not disclose the new figure.
Originally, the construction of two new units was supposed to cost 2.8 billion euros.
Newspaper Hospodarske Noviny reported earlier this year the project would require an additional 500 million euros.
The government has a 34 percent stake in Slovenske Elektrarne and has to approve any budget changes.
Enel signed a deal with Czech energy company EPH in December to sell its stake in Slovenske Elektrarne in two stages, 33 percent initially and the rest after the Mochovce expansion is completed.
$1 = 0.9101 euros Reporting by Tatiana Jancarikova; Editing by Mark Potter