MOSCOW — President Putin has sent a chilling message to world leaders on the eve of the G-8 summit with a threat to aim Russian nuclear missiles at European cities for the first time since the Cold War.

In comments that seemed calculated to cause consternation and division at this Wednesday’s meeting in Germany, the Russian leader said American plans to erect a missile defense shield in Eastern Europe had left him with no choice but to retaliate.

“It is obvious that if part of the strategic nuclear potential of the United States is located in Europe we will have to respond,” he told reporters from G-8 countries in Moscow at the weekend. What kind of steps are we are going to take in response? Of course, we are going to acquire new targets in Europe.”

Mr. Putin’s anti-Western rhetoric has grown more strident since Washington confirmed plans to locate 10 interceptor missiles in Poland and a radar station in the Czech Republic by 2012 — a project he believes is directed at Russia.

With more disputes between Russia and other G-8 members brewing, the strain in East-West relations will overshadow a summit the German hosts wanted to focus on the environment and African poverty.

Despite hopes that an invitation for direct talks with President Bush next month would mollify Mr. Putin’s anger, the Russian president sent out a clear signal that he preferred combat to compromise.

At his last summit with fellow leaders from the Group of Eight industrialized nations, Prime Minister Blair can expect a particularly frosty reception when he meets Mr. Putin on the sidelines of the summit.

The Kremlin is outraged by Britain’s demand to extradite Andrei Lugovoi over the murder of his fellow KGB veteran Alexander Litvinenko, accusing London of exploiting the case for political ends.

Mr. Putin went one step further over the weekend, accusing Britain of providing shelter to terrorists — a reference to the political asylum granted by the courts to Boris Berezovsky, a tycoon and the president’s chief foe, and to Akhmad Zakayev, an envoy of the anti-Russian Chechen rebels. “The suspicion arises that this is a political move made by those who hide terrorists and thieves on their own territory,” Mr. Putin said.

America has backed Britain’s extradition request, although Russia has already rejected it, and Mr. Blair is likely to maintain his support for the American missile shield.

But diplomats suggested that Mr. Putin’s nuclear threat could be borne from a belief that support from other G-8 countries — particularly Germany and Italy — is less solid.