White House officials said that aluminium tubes bought by Baghdad were unusually strong and had been made to such tight specifications that they must have been designed to enrich uranium.

They also said that Iraq had paid a surprisingly high price for the shipment, and went to extreme lengths to keep it a secret.

The tubes are the focus of a dispute between the International Atomic Energy Agency and the Bush Administration. Iraq says that they are for short-range rockets, and Mohamed Elbaradei, head of the agency, has reported that he has seen no evidence to support claims that they are for a centrifuge to enrich uranium.

Colin Powell, the US Secretary of State, will use declassified UN Intelligence surrounding the purchase of the tubes to try again to make the case that they were for use in a nuclear programme. He is due to present a dossier of what the United States says is proof of Iraq’s obstruction and deceit to the UN Security Council next Wednesday.

Ari Fleischer, the White House spokesman, said yesterday that the tubes “far exceed any specifications required for non-nuclear capabilities”. He said: “The preponderance of evidence is that Iraq attempted to procure high-strength aluminum tubes for uranium enrichment. We stand by that statement.”

President Bush said yesterday that the United States would continue to force Iraq to disarm even if President Saddam Hussein goes into exile.

Mr Bush said that he would welcome any move by the Iraqi leader and his “henchmen” to leave the country. But he stopped short of saying that their disappearance would necessarily avoid war.

He said: “No matter how Mr Saddam Hussein is dealt with, the goal of disarming Iraq still stays the same, regardless of who’s in charge of the Government.”

His remarks came before talks with Prince Saud al- Faisal, the Saudi Foreign Minister, who is pressing Washington to help to avoid war by finding a haven for Saddam.

General Powell said on Wednesday that the United States was ready to help Saddam into exile, possibly with the guarantee of immunity from any future charges. Mr Bush did not go as far as General Powell in public, but he sought to reassure the Iraqi people, and the wider world, that if it came to war, “shortly after our troops go, in will go food and medicines and supplies”.

American policy towards Iraq has been to topple Saddam. But by deciding last year to pursue him through the UN, the White House shifted subtly to following a policy of disarming Iraq.

Mr Bush was emphasising yesterday that the two goals have become one, and that American troops may yet be needed to disarm Iraq, depending on what kind of regime followed Saddam.

General Powell is leading the search in Washington for the diplomatic solution. The United States has been contacting Iraqis to try to identify friendly faces and has engaged in psychological operations, including radio broadcasts. The ultimate goal is to oust Saddam without force.

One possible route out of the conflict could be if Saddam used Iraq’s ties with the former Soviet Union to find a haven. Igor Ivanov, the Russian Foreign Minister, has denied that Moscow was trying to persuade Saddam to resign, but he said that it was keeping up contacts with Iraq.

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