Barack Obama sat down for a two-day summit at the Kremlin today, holding out the hope of "extraordinary progress" towards further reductions in the nuclear arsenal of the two old Cold War rivals.

Mr Obama flew into Moscow's Vnukovo airport with his wife, Michelle, and two young daughters to unseasonally cold weather and cloudy skies, although hours of heavy rain came to an end as Air Force One touched down.

After a low-key greeting ceremony, the Obama motorcade sped along a barricaded highway towards the Tomb of the Unknown Soldier, where Mr Obama laid a wreath before getting down to talks with his host, President Medvedev.

The talks will focus on agreeing a successor to the 1991 Strategic Arms Reduction Treaty (Start), which expires in December. A US official confirmed today that there was already a text for the two men to review during their talks, although the summit communiqué will be a statement of intent rather than a full treaty.

As the talks began, Mr Medvedev told his guest that he hoped their summit would close a difficult chapter in US-Russia relations. “We hope that as a result of today’s work, tomorrow’s work and all our bilateral discussions we will close the difficult pages in the history of US-Russian relations and open a new page,” he said.

Mr Obama replied: “If we work hard during these next few days then we will make extraordinary progress that will benefit the people of both countries."

Mr Medvedev said last week that the new treaty could reduce their nuclear arsenals to below 1,700 warheads each, down from the current 2,200 for the US and 2,800 for Russia — a reduction that Mr Obama sees as a fair trade in its own right.

But the Russian leader threw down the gauntlet on the eve of Mr Obama's visit, challenging him to roll back a planned missile shield in Eastern Europe in return for making huge cuts in Russia’s nuclear arsenal.

The challenge came in an interview with Italian media in which he insisted that any agreement would have to include concessions on the European-based missile shield proposed by President Bush.

“We believe that these topics are interrelated and for understandable reasons — because offensive nuclear capabilities do not exist by themselves,” Mr Medvedev said. “If we talk about reduction then we must understand how it correlates with defending against these capabilities, with what means we have for missile defence.”

The two-day visit has been called the “reset summit” after Mr Obama’s promise of a fresh start in relations with Russia. He is keen to revive a relationship that hit a post-Cold War low over Mr Bush’s plans to site radar posts in the Czech Republic and ten interceptor missiles in Poland.

Insiders say that despite Mr Obama’s lack of enthusiasm for his predecessor’s plan he is unlikely to cede much ground while Moscow remains overtly intransigent.

Mr Obama knows that there is no political capital in making concessions while Moscow looks so uninterested in making any of its own. His visit is being closely watched at home by opponents eager to see him commit a foreign policy blunder, and ordinary Americans concerned by the threat that could be posed by a nuclear Iran.

Russia rejects Washington’s insistence that the shield is aimed at a possible Iranian threat, smarting at its intrusion into the post-Soviet region that Moscow regards as its sphere.

Mr Medvedev repeated Russia’s opposition to the shield but said that he believed Mr Obama was ready to compromise as they negotiate cuts in nuclear weapons towards an agreement to replace Start.. “Then we can agree on the basic foundations of a new Start treaty and agree . . . on how we will approach missile defence,” he said.

The visit includes an informal dinner between the Medvedevs and Obamas tonight, while tomorrow Mrs Obama will attend a concert and visit a hospital with Mr Medvedev's wife, Svetlana.

Tomorrow Mr Obama faces a potentially awkward first meeting with Vladimir Putin, the former president who remains, even as Prime Minister, Russia's most powerful politician. Mr Putin was out of Moscow on Monday visiting a combine harvester factory in southern Russia.

In an indication of the strained atmosphere, Russia’s Kremlin-controlled main television channels -- the chief source of news for most Russians -- have played down Obama’s visit and his arrival was not shown live on TV.

“This is being played as essentially a low-key visit that shows the American leadership’s respect for the Russian leadership,” Dmitry Trenin, head of the Moscow Carnegie Centre think-tank, said.“This is not some star coming to town.”

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