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

Russia has put the issue 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.

NATO's anti-missile shield has been repeatedly denounced by Russia which activated a radar warning system against incoming missiles in its exclave of Kaliningrad on the EU's borders last week.

Medvedev recently said Russia may also pull out of a nuclear disarmament deal he had signed with US President Barack Obama in Prague in April 2010 if the US-led alliance goes ahead with its plans.

The shield is the topic of NATO talks held in Brussels on Wednesday, before the 27-member alliance, which includes the Czech Republic, meets Russian Foreign Minister Sergei Lavrov on Thursday.

Lavrov insisted Wednesday Moscow needed legal guarantees from NATO over the missile shield project.

"Our friends in NATO categorically refuse to put on paper in legal form what they say verbally, namely that this missile defence project in Europe is not creating risks for Russia, is not directed against Russia," Lavrov said in the Lithuanian capital Vilnius.

Medvedev is also likely to back a bid from a Russian company to build two nuclear reactors at the Czech Temelin plant.

The project at the plant situated about 120 kilometres (75 miles) south of Prague is estimated to cost 20 billion euros ($28 billion).

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.

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