The talks, which opened Friday, are part of a push by the United States to convince the world it won't start a new arms race.
"The American side has so far failed to produce convincing arguments that would persuade us that it has a clear vision of how to handle international security issues without disrupting the arms control arrangements that have been established over the past 30 years," said Alexander Yakovenko, a spokesman for the Foreign Ministry.
Stephen Hadley, a deputy U.S. national security adviser, said after the first session that the fact the two sides were talking showed progress.
He said the U.S. representatives had "put forward and elaborated on some of the points the president made." Mr. Bush outlined his plans for a national missile defense in a speech last week.
"The Russian side raised some serious and important questions," Hadley said. "We began to give them some answers to their questions."
A prominent Russian lawmaker said earlier that the Kremlin should be flexible in its response to the Bush proposal.
"We should not, gritting our teeth, oppose the very idea of NMD," said Vladimir Lukin, a deputy speaker of parliament and former Russian ambassador to Washington, told Ekho Moskvy radio. "Our stand should be flexible in this case."
Russian Foreign Minister Igor Ivanov, on a visit to Finland, said Moscow was optimistic about the talks' outcome, and he expressed hope that more countries would be consulted.
The high-level American delegation, led by Deputy Defense Secretary Paul Wolfowitz, arrived at the Foreign Ministry on Friday morning for talks with a Russian interagency committee created to shape the Kremlin's response to President Bush's proposal.
In his speech, Mr. Bush committed the United States to building a shield against ballistic missile attack, warning that hostile nations such as Iraq have replaced the Soviet Union as the main threat to the United States and its allies.
Hadley said for Americans who lived through the Gulf War and saw the effect of Scud missiles, "the threat has a certain reality and urgency that maybe is not shared. That's one of the things we want to talk about."
Russia says the ABM treaty is a cornerstone of international security and wants it preserved as a barrier to bigger nuclear arsenals. The treaty bans testing of anti-missile rockets, limits radar capabilities and prohibits the signatories from involving allies in deploying anti-missile rockets.
Russia reacted with surprising calm to Mr. Bush's announcement last week that the United States wanted to go ahead with its missile shield plans. President Vladimir Putin welcomed Mr. Bush's pledge to consult with other nations on missile defense and urged the United States to wrk with Russia on arms issues.
U.S. envoys held talks with NATO members and other allies this week, and a delegation headed by U.S. Deputy Secretary of State Richard Armitage was holding talks with Indian officials Friday on missile defense and other issues.
"I was honored to present President Bush's thinking on a new strategic framework, which includes many elements, including our willingness to unilaterally reduce our nuclear arsenal below the levels of START II," Armitage said after meeting Indian Defense and External Affairs Minister Jaswant Singh.
In his speech last week, Mr. Bush did not say how far he was willing to cut the U.S. stockpile of 7,200 nuclear weapons. Under START II, the United States already is committed to reducing the arsenal to 3,500, and Russia has sought even deeper cuts.
In Ankara, Undersecretary of State Marc Grossman met with Turkey's prime minister and foreign minister and said the United States hoped to involve as many countries as possible in the missile defense system.
"We would like to see the day when all countries are able to protect themselves from terrorism or blackmail," he said.
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