The US issued a bleak warning to Britain and other key allies last night that the war against international terrorism could mean conflict with nations possessing weapons of mass destruction.

As six RAF Tornado jets left RAF Leeming, North Yorkshire, for the Middle East, US deputy Defence Secretary Paul Wolfowitz told Nato defence ministers that there was an alarming connection between states which sheltered terrorists and those trying to develop nuclear, biological and chemical capabilities. Britain's Defence Secretary, Geoff Hoon, said: "The point has been made that there are some links between countries that harbour terrorists and those that allow the development of weapons of mass destruction."

Although no states were named, their comments would appear to point directly to Iraq. Mr Wolfowitz has reportedly been arguing strongly within the US administration that the war on terrorism should be extended to Saddam Hussein's regime.

The Tornado F3 Aircraft from RAF Leeming joined more than 20,000 UK troops that have ostensibly been deployed to train alongside Omani forces. But they and 21 Royal Navy ships and 50 other RAF aircraft are well placed if action in the war on terrorisism is declared.

Following the discussions in Brussels, a sombre Nato Secretary General, Lord Robertson, said the alliance would need to adjust their military thinking to cope with the new threat.

"The campaign against terrorists will be long, arduous and will require radical new thinking. Adaptability, non-conventional thinking, patience and determination are key elements for this campaign."

Mr Wolfowitz brought no specific plans for military strikes against Afghan-istan - accused of harbouring Osama bin Laden. The first operations may simply be to gather more intelligence.

Mr Wolfowitz also said the US was not yet ready to present its evidence that Saudi-born bin Laden was behind the terrorist attacks on the World Trade Centre and the Pentagon.

Nevertheless, speculation that the US-led coalition was moving closer to military strikes was fuelled by the announcement from Downing Street that Tony Blair had summoned a Cabinet meeting for 5pm today.

In Washington, US Defence Secretary Donald Rumsfeld warned that the coming conflict against terrorism would last "not five minutes or five months", but would go on for years.

He said: "There is not going to be a D-Day as such.

"This is not something that begins with a significant event or ends with a significant event. It is something that will involve a sustained effort over a good period of time.

"It is by its very nature something that cannot be dealt with by some sort of massive attack or invasion. It is a much more subtle, nuanced, difficult, shadowy set of problems."

He warned that public opinion needed to be prepared to accept possible casualties. "It will not be an antiseptic war, I regret to say. It will be difficult. It will be dangerous. The likelihood is that more people may be lost."