"That will complicate enormously the situation. Unilateral action of that nature I don't think will contribute to what is the aim of everybody," Solana said.

"I don't think at this point in time that it is worth thinking about that," he said.

His warning, expressed during an interview on Britain's ITV network Sunday, came after US Secretary of State Condoleezza Rice for the second time refused to say whether Washington would deter an attempted Israeli strike on Iran's nuclear facilities.

Last month US Vice-President Dick Cheney suggested that Israel "might well decide to act first" in launching an attack on Iran, but Rice would not comment on what advice she would give to Ariel Sharon when she meets him.

"I'm not going to speculate," she told BBC's Breakfast with Frost on Sunday. Instead, she put the onus on Tehran to prevent any strike, saying "the Iranians need to live up to their international obligations so we don't face any such point."

But Cheney, when questioned about Cheney's warning, said that it would "be something I would not like to see taking place. That would be a mistake."

Asked if he agreed with UK Foreign Secretary Jack Straw that a US military action against Iran was "inconceivable," he said he believed that military action was "very difficult to conceive."

"I don't think that the United States has at this point of time the wish or the will or the capability to do that," said the EU's high representative.

At a joint press conference in London Friday, Straw, like Rice, refused to say whether he would deter or encourage an Israeli attack on Iran.

The British foreign secretary also went further in putting the onus on Iran, suggesting that Tehran also needs to change its position in not recognizing Israel.

"It cannot go on, if it (Iran) wishes to be a full member of the international community. Denying the right of one member of the United Nations to exist is a fundamental destabilizing aspect of the Middle East situation," Straw told journalists.