THE United States and Russia are to slash their nuclear stockpiles by up to a third as part of a move to improve relations between the former Cold War foes.
The weapons deal was agreed in principle after four hours of talks at the Kremlin between US president Barack Obama and Russia's Dmitry Medvedev. Moscow also said it would allow the US to fly troops and weapons across its territory to Afghanistan.
Mr Obama said he wanted to end the "suspicions and rivalry of the past" that had dogged relations between the superpowers.
The deal on arms reduction means the world's two largest nuclear powers – which control 90 per cent of global stockpiles between them – will begin reducing their numbers of nuclear warheads to between 1,500 and 1,675 within seven years of a new treaty being signed. Strategic delivery systems will also be cut to between 1,000 and 500.
Opponents of Britain's plans to replace Trident said it showed the need for a UK deterrent was diminishing.
But the two leaders remained deadlocked on the thorny issue of the proposed US missile defence system in Eastern Europe – what Russia sees as its own backyard. The US insists its system would be aimed not at Russia but potential rogue nuclear states such as Iran or North Korea.
Both presidents tried to put on a show of unity at a joint press conference in the gilded hall at the Kremlin.
Mr Obama hailed the agreement on nuclear stockpiles, which will mean both sides scaling down their weapons by some 1,000 each.
"We must lead by example and that's what we are doing here today," he said. "We resolve to reset US-Russian relations so that we can co-operate more effectively in areas of common interest."
On what was his first trip to Russia as president, he said both countries had been hampered in making progress in their relations by old "bureaucracies".
Mr Medvedev also welcomed the deal, saying, "We hope that, as a result of our conversations today and tomorrow… that we will close a number of difficult pages in Russian-American relations and turn a new page."
He also joked that the pair had no choice but to sit inside and hold talks, due to Moscow's unusually cold temperatures. "Even the weather favours our discourse today, as it is cold outside," he said.
In another signal of easing tensions, Russia said it would allow US troops and weapons to be flown over its airspace for missions to Afghanistan, saving the Americans potentially dangerous and expensive journeys through Pakistan.
In the aftermath of the 9/11 terrorist attacks in 2001, Russia had allowed "humanitarian" flights to transit its airspace, but it stipulated only "non-lethal" goods could be transported.
There was also an agreement on a resumption of military co-operation, suspended after last year's Russian invasion of Georgia, and the lifting of restrictions on Russia's importation of some US pork products imposed because of swine flu.
However, one outstanding issue still threatens to derail further talks and co-operation.
The Russians oppose the US's proposed missile defence shield, which is to be based in Poland and the Czech Republic.
Mr Obama yesterday tried to reassure Mr Medvedev, saying:
"There is no scenario in our perspective in which this missile defence system would provide any protection against a mighty Russian arsenal."
It is a subject likely to come up this morning when Mr Obama has breakfast with Russian prime minister Vladimir Putin, who is widely regarded as still the de facto president.
The atmosphere at those talks may be a little frostier because, ahead of his trip to Moscow, Mr Obama appeared to refer to Mr Putin as harbouring an old Cold War approach.
He said: "I think that it's important that, even as we move forward with President Medvedev, that Putin understands the old Cold War approach to US-Russian relations is outdated… Putin has one foot in the old ways of doing business and one foot in the new."
In the Kremlin yesterday, Mr Obama gave a more positive assessment of Mr Medvedev. He said: "Throughout our interactions, I found him to be straightforward, professional. He is clear about interests of the Russian people, but he is also interested in finding out what the interests of the United States are."
For his part, Mr Medvedev praised the US president for appearing to listen to Russia. He admitted the positioning of the US defence shield remained a "complicated" topic but added: "Our American partners – in contrast with what was happening in the past years – have taken a pause and are studying the situation and based on this will formulate their final position.
"So at least it is a step forward to reach a compromise on this quite difficult problem."
Analysts welcomed the nuclear arms agreement, although some cautioned that further hurdles remained.
Mark Fitzpatrick, senior fellow for non-proliferation at the International Institute for Strategic Studies, said it was important to reach agreement so a new deal could be signed before an existing strategic arms reduction treaty expired in December.
"The cuts themselves are not that significant. But it does get the ball rolling because arms control has been dead in the water for the last eight years. There's now a prospect for further cuts in the upcoming years," he said.
Kate Hudson, chairwoman of the Campaign for Nuclear Disarmament, said campaigners wanted arms reduction to go further, but it was a good start.
"It's the first time that Russia has said that it agrees with the goal of global abolition, which is very significant," she said.
Fyodor Lukyanov, editor of the journal Russia in Global Affairs, said the presidents were agreeing on the easy issues, such as Afghanistan and the nuclear treaty. "On other topics like Iran and post-Soviet countries, compromises will not be enough and one side must change position, which is therefore more complicated," he said.
Masha Lipman, a political analyst at the Carnegie Moscow Centre, said allowing US troops to use Russian airspace to transport weapons to Afghanistan was perhaps the most significant development yesterday.
She said: "It is certainly progress and clearly an act of goodwill, although obviously Russia will benefit if the US operations succeed."
The nuclear weapons deal reached in Moscow put pressure on Gordon Brown to scrap plans to renew Trident.
The SNP's Westminster leader Angus Robertson said the agreement between the big powers "underlines the utter madness of UK government plans to proceed with Trident renewal".
Liberal Democrat leader Nick Clegg said it was time for Britain to play its part by ruling out a replacement for Trident.
Great powers' mission to repair their relations is good news for everyoneTHE agreement between Russia and the United States to cut the number of nuclear weapons each points at the other is significant – but hardly for the reasons stated on the box.
In strategic terms, chopping those nuclear arsenals down from 2,200 to 1,675 warheads apiece means they can obliterate each other perhaps seven times over, rather than the previous ten.
The real significance is in the symbolism of the deal. After eight years of strife that began with the arrival of Vladimir Putin in Moscow and George Bush in Washington, Barack Obama and Russian president Dmitri Medvedev have agreed to start talking again.
Their task is to repair relations between Moscow and Washington, which had sunk to hostility not seen since the bad old days of the Cold War.
That hostility was stoked by the war in Chechnya, America's invasion of Iraq, US support for Ukraine's pro-democracy Orange Revolution, the bullying ways of Russian gas giant Gazprom, and America's growing influence in eastern Europe and Central Asia, which Moscow considers its "backyard."
Things bottomed out last August when Russia invaded Georgia, a US ally vital because it carries the pipelines that give America access to the oil and gas riches of Central Asia.
But the global recession has shown both nations that, in this interconnected world, a go-it-alone foreign policy is simply not feasible.
Neither man expects the other to launch a nuclear strike, nor that the new START treaty, due to be signed in December, will remove the ability to do so.
A new Start treaty promises, in fact, a new start. Joint co-operation on nuclear weapons is a signal of joint co-operation elsewhere.
Iran is the immediate focus. Having battled Islamic insurgents in Chechnya, Russia is as worried as America at the prospect of a nuclear-armed Iran. Both governments want to forestall what they fear will otherwise be a nuclear arms race in the Middle East.
For Mr Obama, Russian co-operation is vital for his foreign policy blueprint, which involves solving an interlocking series of conflicts stretching from Israel and the Palestinians through Iraq to Afghanistan.
The Kremlin simply wants some peace and quiet. It will co-operate elsewhere if the United States goes slow on installing its missile shield in eastern Europe, drops its support to bring Georgia and Ukraine into Nato, and agrees to share Central Asia's oil and gas reserves.
None of which means Mr Obama and Mr Medvedev will be friends. But the two powers who together account for 90 per cent of the world's nuclear arsenals have agreed, for the moment, to swap confrontation for negotiation. In a turbulent and uncertain world, that should be good news for everyone.
• Chris Stephen spent five years as The Scotsman's Moscow correspondent.
Read analysis of the US-Russian relationship here