Russian President Dmitry Medvedev arrived in Prague for a two-day visit Wednesday amid mounting tensions between Moscow and NATO over the alliance's planned missile defence shield.

Medvedev's plane landed at 19:20 (1820 GMT), an AFP photographer said.

Moscow has put the missile shield on the agenda of Medvedev's second visit to the Czech capital, side by side with "a major package" of bilateral business deals and the global financial crisis.

Russia, which has fervently denounced the shield, activated a radar warning system against incoming missiles in its exclave of Kaliningrad on the EU's borders last week.

NATO Secretary General Anders Fogh Rasmussen said Wednesday such a move was "a waste of valuable money" as the alliance still wants a deal with Russia to cooperate on the system.

His words followed a request from Russia's Foreign Minister Sergei Lavrov for NATO to provide legal guarantees that "this missile defence project in Europe is not creating risks for Russia, is not directed against Russia."

In Prague, Medvedev is also likely to back a bid from a Russian company for a 20-billion-euro ($28-billion) contract to build two nuclear reactors at the Temelin plant situated about 120 kilometres (75 miles) south of Prague.

Russia's Atomstroiexport has teamed up with Czech technology supplier Skoda JS for the bidding, facing competition from US energy giant Westinghouse and France's Areva.

The winner is due to be announced in 2013, and the new reactors are scheduled to start working around 2025.

On Wednesday evening, the Russian presidential couple will dine with Czech President Vaclav Klaus and his wife.

Medvedev will hold the key talks Thursday, including a meeting with Czech Prime Minister Petr Necas.

The visit follows last Sunday's general election in Russia, won by Prime Minister Vladimir Putin's ruling party despite a serious loss of support in the vote slammed by the Russian opposition and western observers as unfair.

Former Soviet leader Mikhail Gorbachev on Wednesday called for Russia's elections to be re-run due to fraud, as the opposition vowed new rallies contesting the results despite mass arrests.

Putin said in September he would run for president in March 2012, while Medvedev is expected to take over as the country's prime minister.