In between, Bush and the other leaders planned to discuss issues ranging from Africa aid to trade and Lebanon.

The rhetoric began this year when the US chose the Czech Republic and Poland as the missile defense sites and roused Russian suspicions.

Bush is visiting both countries on his eight-day European trip. He has insisted the shield is planned to block any future Iranian nuclear missiles, not Russian ones.

Putin spokesman Dmitri Peskov said these were "insufficient explanations" and promised "uncomfortable consequences," such as possible missile retargeting, if the shield is deployed "next to our borders" without more acceptable ones.

But, he added: "Russia is the last country in this world who is thinking about confrontation or starting another Cold War."

Simon Serfaty, director of European Studies at the Center for Strategic and International Studies, said Putin is overplaying his hand.

"This is a passing moment of post-imperial nostalgia for Russia," he said.

Stephen Sestanovich, a Russia expert at the Council on Foreign Relations, said Putin needs to tread carefully because Russia's relations with Europe are taking a dive, too. "Will the G-8 meetings deepen this crisis? Almost surely not," Sestanovich said. "The G-8 is not a forum for deepening crises."

The summit is being held under tight security in Heiligendamm on northern Germany's Baltic coast. Some 800 protesters made it to a 7-mile, razor-wire fence encircling the summit town on Wednesday, while 10,000 more reached areas where demonstrations had been banned.

In addition to the Czech Republic, Germany and Poland, Bush also intends to visit Italy, Albania and Bulgaria.

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