US Secretary of State Hillary Clinton on Monday backed a bid by US energy giant Westinghouse to build two new units at the Czech Temelin nuclear plant worth at least $10 billion (7.67 billion euros).

"We are not shy about pressing the case for Westinghouse to expand the Temelin nuclear power plant because we believe that company offers the best option for the project in terms of technology and safety," Clinton said.

The US giant faces stiff competition from Russia's Atomstroiexport bidding together with a Russian-owned Czech company.

France's Areva, a third bidder, was ruled out of the tender but has filed an appeal against the decision with the Czech UOHS anti-competition watchdog.

The new units due to come online in 2025 aim to raise the share of nuclear power in the Czech energy mix to 50 percent from the current 30 percent produced by Temelin and by another plant in the southern village of Dukovany.

Prague is looking to nuclear power as its communist-era coal plants face likely closure owing to tighter EU regulations on greenhouse gas emissions.

"We are encouraging the Czech Republic to diversify its energy sources and suppliers in ways that are economically sustainable and environmentally sound," the top US diplomat added.

An ex-Soviet bloc country of 10.5 million which joined NATO in 1999 and the European Union in 2004, the Czech Republic now depends on Russia for 60 percent of oil supplies, 70 percent of gas supplies and 100 percent of nuclear fuel supplies, according to US sources.

Westinghouse's victory "would clearly enhance Czech energy security and further the nuclear collaboration between our two countries," Clinton said following talks with Czech counterpart Karel Schwarzenberg.

"It would create jobs and economic opportunity for Czechs and Americans (and)... ensure the new facility would be built to the highest international standards, using a model that has already been approved by EU and international energy agency regulators," she added.

"We clearly hope that Westinghouse will receive the utmost consideration as this process moves forward," said Clinton, on her first solo trip to this eastern European nation as secretary of state.

Bids for the new reactors were placed in July, and the winner is due to be announced in late 2013, with the two units worth an estimated 200-300 billion koruna (8-12 billion euros, $10-15 billion).

Planned in the communist era and launched in 2000, the Temelin nuclear facility has been repeatedly criticised by Vienna over safety concerns. It lies about 120 kilometres (75 miles) south of Prague, but only about 60 kilometres from the Austrian border.

It includes two Russian-type VVER pressurised-water reactors, each with an output of 1,000 megawatts, and may also become a thorn in the side of Germany which has vowed to shut down its own nuclear reactors by 2022.

The Americans say if the US giant is awarded the contract it could create some 9,000 jobs in the United States plus others in the Czech Republic.

Clinton, on the first leg of a five-day Europe trip, also met with Czech Prime Minister Petr Necas and the leftist opposition leaders during her whirlwind 12-hour visit.