"The first step will still have to be to clarify exactly what President (Vladimir) Putin meant," chief NATO spokesman James Appathurai told reporters, when asked how the alliance would respond to the apparent move. "I have seen quotes from presidential advisors saying: 'Well, we only mean in six months', I have heard some else tell me that he subsequently said they only mean in one year," he said.
"There will clearly be a discussion within NATO, there will clearly be a discussion between capitals and the Russian Federation on what they mean."
Making his last state of the nation speech in Moscow, Putin said Thursday that Russia could pull out of the 1990 Conventional Forces in Europe (CFE) treaty until all of NATO's current members ratified it.
"It would be appropriate to announce a moratorium on Russian adherence ... until it has been ratified by all NATO countries without exception," he said.
NATO Secretary General Jaap de Hoop Scheffer said the 26 member countries had received the news with "concern, grave concern, disappointment and deep regret because the allies are of the opinion that the CFE treaty is one of the cornerstones of European security."
But German Foreign Minister Frank-Walter Steinmeier called for calm. "The arithmetic of the Cold War, with its numbers of armed vehicles, missiles and troops on each side, just doesn't add up any more," he said. "We must avoid an escalation."
Europeans call for calm
"What we need is not less disarmament and fewer arms controls, we need more," said Steinmeier, whose once-divided country was the frontline for the Cold War.
In Berlin government spokesman Thomas Steg called for continued dialogue, while adding that "we are strongly convinced that threats do not help."
In France foreign ministry spokesman Jean-Baptiste Mattei called for Russia to go back on its decision, calling the CFE treaty "a cornerstone of security in Europe."
He said that debate on the treaty and the US anti-missile plan that triggered Putin's move should continue in the NATO-Russia joint council to overcome Moscow's suspicions.
The CFE treaty was signed in 1990 in Paris by the countries of the North Atlantic Treaty Organization (NATO) and the former Warsaw Pact to limit military hardware in the region.
It was adapted in Istanbul in 1999 following the collapse of the Warsaw Pact, in order to limit deployments on a country-by-country basis.
NATO states have refused to ratify the new pact on the grounds that Moscow has failed to honour commitments made in Istanbul to withdraw Russian forces from the former Soviet republics of Georgia and Moldova.
Increased threat of mutually assured destruction
President Putin reiterated his belliegernt stance when he warned of an increased threat of mutually assured destruction in a meeting about the planned US missile shield with Czech President Vaclav Klaus.
"The increase of the threat of mutual harm to one another, and possibly of destruction, will grow many times over," Putin said, adding the system's proposed bases in the Czech Republic and Poland would violate Europe's security apparatus.
Although the US plans have been known for years, Russia has increased its rhetoric in recent months after the Czech Republic and Poland, Eastern European countries Moscow considers its sphere of influence, entered talks to house elements on their territory.
US Defence Secretary Robert Gates visited Putin and other officials in Moscow earlier this week to invite Russia to join the project, but apparently made little progress.
Washington says the shield is designed to protect against threats from Iran and North Korea and that its 10 interceptor missiles could not defend against Russia's thousands of warheads.
Russia claims to be real target
Russia has said it is the target of the shield, and Putin told Klaus he was ready to invite specialists from the Czech Republic and Poland to show neither Iran nor North Korea had missile systems demanding the defence system.
Washington, for its part, says both North Korea and Iran either have or are trying to acquire atomic bombs and could in 10 years' time have missiles that threaten Europe.
Klaus told Russian news agencies after his talks with Putin that he had been unable to explain the Czech arguments for the shield. "I assured the president the Czech side didn't have the slightest intention for the radar bases (proposed for Czech territory) to become a threat to Russia," Klaus said.
"That's understandable - the Czech Republic won't control the stations," Putin was quoted as saying in response.
In a meeting where Putin reminded Klaus his country received 75 per cent of its natural gas from energy-rich Moscow and had recently signed an agreement lasting till 2035, Putin told the Czech leader the shield was similar to putting nuclear missiles on European territory.
Putin said he hoped the Czech Republic would advance Russian-EU relations as European Union president in 2009. "I have a very wide circle of questions and problems and we are glad for the opportunity to exchange opinions," he added. But regarding the shield, he added that "as head of state I would have to say yes, relations will worsen."
"We won't raise an hysteria over this, we'll simply take the necessary measures," the Russian leader said.