 The United States has rejected fresh concerns raised by Moscow about its planned missile defence system.
The State Department statement came after Russian PM Vladimir Putin said the US plans were holding up a new nuclear disarmament treaty.
The statement said the two issues were completely separate, and discussions would continue separately. Russia and the US are yet to find a successor to the Cold War-era Start I treaty, which expired on 5 December. Analysts say Moscow wants a clause in the new treaty that would limit the scale of any US defence shield. The US has shelved plans for missile defence stations in Central Europe, but intends to use a sea-based system. The BBCs Imtiaz Tyab in Washington says it is clear from Mr Putins comments Russia still sees any missile shield as a threat - one it is now pledged to counter. But the hardening of Russias position must be frustrating for US President Barack Obama, our correspondent says, after the concessions he has made. Keeping the balance The US statement said that Washington and Moscows joint position recognising the inter-relationship between defensive and offensive weapons systems had not changed. "While the US has long agreed that there is a relationship between missile offence and defence, we believe the Start follow-on agreement is not the appropriate vehicle for addressing it," it said. "We have agreed to continue to discuss the topic of missile defence with Russia in a separate venue." Earlier Mr Putin said the US plans would allow them to do whatever they wanted and thus upset the balance. He said that "to preserve the balance, we must develop offensive weapons systems", but did not specify what kinds he had in mind. Earlier this month, President Dmitry Medvedev said Russia would continue to develop new warheads, delivery vehicles and launchers despite the disarmament talks, describing this as "routine practice". Russia and the US are negotiating in Geneva on the details of a new treaty. Last week, the Russian foreign minister said a deal was very close. The 1991 Start I treaty led to deep cuts in nuclear arsenals by Washington and Moscow. Both sides have agreed to continue observing Start I until they reach a new agreement. Under a joint understanding signed in July, deployed nuclear warheads should be cut to fewer than 1,700 on each side within seven years of a new treaty - a huge cut on Soviet-era levels. Nonetheless, between them the two countries will retain enough firepower to destroy the world several times over. The BBCs Rupert Wingfield-Hayes in Moscow says that Russias nuclear arsenal is the only part of its military that remains world-class, and therefore it fears that it could be disadvantaged by cuts to nuclear capability. Mr Putins comments could be a negotiating ploy, rather than a reversal of Russias commitment to a treaty, our correspondent says. Analysts in Moscow think what Mr Putin really wants is a commitment from Washington to only deploy a small-scale missile defence system, that would be effective against Iran and North Korea but would not neutralise Russias nuclear missile force, he adds.
ANALYSIS
Rupert Wingfield-Hayes, BBC Moscow correspondent Russias government said until just a few days ago that these strategic arms reduction treaty talks were in their final stages, that they were perhaps just a couple of weeks away from signing a new document. And now suddenly Mr Putin has come out with this statement, which really does put a spanner in the works. It shows just how nervous Russia is about the idea of a US missile defence shield, despite the fact President Obama in September said they were going to scrap land-based missile defence in Europe. The US plans to build another system; the Russians dont know exactly how thats going to affect them and how it may neutralise their nuclear deterrent. I think Mr Putin is voicing a concern that is held by many experts in this country. | 
