Washington: In a major shift based on a reassessment of the threat from Iran, US President Barack Obama Thursday shelved plans for a missile shield in Eastern Europe, the cause of a Cold War-style row with Russia.

Obama decided to replace the shield, the brainchild of former US president George W. Bush, with a more mobile system targeting Iranian short-range and medium-range missiles, initially using sea-based interceptors.

“Our new missile defense architecture in Europe will provide stronger, smarter, and swifter defenses of American forces and America’s allies,” Obama said at the White House.

The decision however risked alienating US allies in the former Soviet bloc and infuriated Obama’s Republican foes, who accused him of appeasing Moscow and of showing dangerous weakness.

Sensitive to claims he is weak on national security and was sending the wrong kind of signal towards Iran, the president insisted the new plan made American allies more secure.

“This new approach will provide capabilities sooner, build on proven systems and offer greater defenses against the threat of missile attack than the 2007 European missile defense program,” he said.

The dramatic move followed a shift in intelligence assessments of Iran’s ballistic program, which concluded the most immediate threat was Tehran’s short- and medium-range arsenal, not yet-to-be-developed long-range missiles.

“Our clear and consistent focus has been the threat posed by Iran’s ballistic missile program and that continues to be our focus and basis of the program that we’re announcing today,” Obama said.

The Bush-era system would have involved building a radar system in the Czech Republic and basing missiles in Poland — a scenario which infuriated Russia and became an impediment to better US-Russia relations.

Critics argued the system could not be proven to work, was focused on a non-existent threat from Iranian long-range hardware and needlessly angered Russia.

Defense Secretary Robert Gates said under the reconfigured system, more mobile SM-3 interceptor missiles would initially be deployed on ships, while the military developed a land-based system.

“The second phase, about 2015, will involve fielding upgraded land-based SM-3s,” he said.

Consultations have begun with allies, starting with Poland and the Czech Republic, about hosting the land-based version, he said.

The White House denied the decision was part of a quid pro quo to entice greater Russian cooperation on issues like Iran’s nuclear program and Afghanistan.

“Absolutely not,” said Obama spokesman Robert Gibbs, insisting the president had been motivated by military and strategic imperatives and not by Russia’s charges that the proposed Eastern European shield threatened its security.

“This is not about Russia,” he said.

Russian President Dmitry Medvedev, due to see Obama at the UN General Assembly and the G20 summit in Pittsburgh next week, hailed the decision, saying it could boost anti-missile cooperation between Moscow and Washington.

“I am ready to continue dialogue,” he said, adding that “Washington’s declaration today shows that there are good conditions” on the ground for joint anti-missile action.

Konstantin Kosachev, head of the Russian lower house of parliament’s foreign affairs committee. said “Russia has been waiting for this for a long time.”

“The Obama administration is starting to understand us,” he said, while Moscow also denied the US decision was part of a secret US deal with Russia.

Czech Prime Minister Jan Fischer said he learned of the plan during a late-night call from Obama.

“The Czech Republic has acknowledged this decision,” he said.

But Mirek Topolanek, who was prime minister when Prague agreed to co-host the shield, said Obama’s move was “not good news for the Czech state, for Czech freedom and independence.”

In Poland, former president and Nobel laureate Lech Walesa said it might be time rethink close ties with the United States.

There was also fury among Republicans, who tried to use the decision to brand Obama weak on national security.

The number two Senate Republican Jon Kyl, called the move “dangerous and short-sighted,” and said it left the United States vulnerable to a growing threat from Iranian long-range missiles.

Obama’s defeated Republican election foe John McCain complained that the decision was “seriously misguided.”