A Czech antitrust watchdog on Tuesday banned state-run power group CEZ from signing a deal on the construction of two new units at its Temelin nuclear facility pending a complaint from France's Areva.

"The UOHS anti-trust office issued an... injunction on November 19, banning CEZ from signing a contract to complete the Temelin plant" in the southern Czech Republic, UOHS head Petr Rafaj told AFP.

Areva was ruled out of the tender to build the units by CEZ on October 5, allegedly over failing to set a fixed price for the project and a completion deadline.

"At the same time, the UOHS rejected Areva's proposal to suspend the tender," Rafaj added.

This means CEZ can go on assessing the bids submitted by rivals US giant Westinghouse and Atomstroiexport for the contract worth an estimated 200-300 billion koruna (8-12 billion euros, $10-15 billion).

The bids were placed in July, and the winner is due to be announced in late 2013.

The watchdog declined to say how long the proceedings may last.

"They will definitely be the longest proceedings in the office's history, so we cannot calculate their length by merely adding 60 days to the date they were launched," Rafaj said.

The two units, due to be finished by 2025, will raise the share of nuclear energy in the Czech energy mix to about 50 percent from the current 30 percent produced by Temelin and another CEZ-operated nuclear plant in the southern village of Dukovany.

Temelin, about 120 kilometres (75 miles) south of Prague, but only about 60 kilometres from the Austrian border, has been repeatedly criticised by Vienna over safety concerns.

It may also become a thorn in the side of Germany, which has vowed to shut down its own nuclear reactors by 2022.

The Czech government, which owns two-thirds of CEZ, is betting on nuclear power as its communist-era coal-fired plants are likely facing closure amid tighter regulations on greenhouse gas emissions.

Planned in the communist era and launched in 2000, the existing Temelin facility includes two Russian-type VVER pressurised-water reactors, each with an output of 1,000 megawatts.

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