Mr Putin has criticised the original US missile shield plans
US plans for a missile defence shield are holding up a new nuclear disarmament treaty, Russian Prime Minister Vladimir Putin has said.
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.
Asked by a reporter what was the biggest problem blocking a new treaty, Mr Putin said: "What is the problem? The problem is that our American partners are building an anti-missile shield and we are not building one."
"By building such an umbrella over themselves, our [US] partners could feel themselves fully secure and will do whatever they want, which upsets the balance," the Russian premier added.
Rupert Wingfield-Hayes, BBC Moscow correspondent
Russia's 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 don't know exactly how that's 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.
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 BBC's Rupert Wingfield-Hayes in Moscow says that Russia's 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 Putin's comments could be a negotiating ploy, rather than a reversal of Russia's 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 Russia's nuclear missile force, he adds.