"The Iranians just need to know that the free world is working together to send a very clear message: Don't develop a nuclear weapon," he said as he met with Polish President Aleksander Kwasniewski at the White House.

"And the reason we're sending that message is because Iran with a nuclear weapon would be a very destabilizing force in the world," said Bush, who told reporters he would bring that message on his late February trip to Europe.

Rice said during her first trip to Europe since taking her new post that Tehran must face possible UN sanctions if it rejects diplomatic overtures aimed at ending the dispute over its atomic programs.

"I don't know that anyone has said that as clearly as they should to the Iranians," she told Fox News in an apparent message to British, French and German leaders who have spearheaded talks with Tehran.

"I'm very pleased with the response that European leaders have given to Dr Rice on this issue," Bush said. "It's important we speak with one voice."

The United States accuses Iran of trying to obtain nuclear weapons under cover of developing a civilian atomic energy program and has not excluded a military option against Tehran.

But while Washington wants to take the case to the UN Security Council, the Europeans have favored seeking to resolve the issue through talks.

The United States has so far supported the diplomatic efforts, which have focussed on getting Iran to promise not to make the bomb in return for trade privileges with the 25-nation bloc.

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