The United States has hinted that it may attack Iraq without the help of Britain, as Prime Minister Tony Blair is facing enormous opposition from his country's anti-war forces.

"This is a matter that most of the senior officials in the government discuss with the UK on a daily or every-other-day basis," Defence Secretary Donald Rumsfeld told a Pentagon press conference on Tuesday.

"And I had a good visit with minister of defence of the UK about an hour a go. Their situation is distinctive to their country, and they have a government that deals with parliament in their way, distinctive way. And what ultimately will be decided is unclear...

"There is the second issue of their role in a post-Saddam Hussein reconstruction process or stabilisation process, which would be a different matter," he said.

Later, after reports that British officials were surprised by his comments, Rumsfeld said in a statement that the main point of his press conference was that "obtaining a second UN Security Council resolution is important to UK".

"In the event a decision to use force is made, we have every reason to believe there would be a significant military contribution from the UK," the statement said.

Asked during the press conference whether the US would consider going to war without Britain, Rumsfeld said, "That is an issue that the President [George W Bush] will be addressing in the days ahead, one would assume."

Rumsfeld's comments came after the Pentagon tested the most powerful non-atomic bomb in history -- a 21,000-pound device nicknamed the 'Mother of All Bombs'. Officially it is called the Massive Ordnance Air Blast weapon.

Referring to the impact the testing could have, Rumsfeld said: "There is a psychological component to all aspects of warfare.

The goal is to not have a war. The goal is to have the pressure... so great that Saddam Hussein cooperates.

"Short that, an unwillingness to cooperate, the goal is to have the capabilities of the coalition so clear and so obvious that there is an enormous disincentive for the Iraqi military to fight, and there is an enormous incentive for Saddam Hussein to leave and spare the world a conflict."