The United States has rejected fresh concerns raised by Moscow about its planned missile defense system.

The State Department statement came after Russian PM Vladimir Putin said the U.S. 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 U.S. 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 U.S. defense shield.
The U.S. has shelved plans for missile defense stations in Central Europe, but intends to use a sea-based system.
The BBC's Imtiaz Tyab in Washington says it is clear from Mr. Putin's comments Russia still sees any missile shield as a threat - one it is now pledged to counter.
But the hardening of Russia's position must be frustrating for U.S. President Barack Obama, our correspondent says, after the concessions he has made.
The U.S. statement said that Washington and Moscow's joint position recognizing the inter-relationship between defensive and offensive weapons systems had not changed.
“While the U.S. has long agreed that there is a relationship between missile offence and defense, 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 defense with Russia in a separate venue.”
Earlier Mr. Putin said the U.S. 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 U.S. 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.
(Source: BBC)