Colin Powell will not rule out war against Iraq

It is not known whether Saddam Hussein's regime has been developing weapons of mass destruction since the departure of UN weapons inspectors left in 1998.

There has been speculation that some form of biological and even nuclear weapons programme continues in Iraq.

But many fear an attack on Iraq could destabilise the region, drawing in neutral countries and stretching the allied coalition to breaking point.

Critics of US policy want the allies to concentrate on helping Afghanistan rebuild its infrastructure.

Sir Michael told the Royal United Services Institute that terrorism could only be defeated by winning "hearts and minds".

Excessive optimism

The growing division between the UK and US has echoes of the Vietnam era.

The US eschewed the UK's "hearts and minds" approach to insurgents in Malaya, adopting a strategy in Vietnam dubbed "search and destroy".

Sir Michael also warned of excessive optimism about successes against the Taleban.

He reminded the audience that the war was not conventional and could not be measured in territory won.

Politicians and the media should take a longer-term view of events on the ground where the situation could often be tenuous, he said.

Enemy focus

"Simple victory over the Taleban is not the end stake that we seek.

"We must continue to focus on the enemy rather than on the ground taken."

Sir Michael maintained that in the short term the al-Qaeda network was still capable of terrorist atrocities.

And he said the UK had to make a choice which it could not dodge - either broadening the war or concentrating on aid and rebuilding in Afghanistan.

Peacekeeping mission

But the Ministry of Defence (MoD) has dismissed as "absolutely without foundation" reports that the UK has accepted the task of leading a multinational peacekeeping force in Afghanistan.

American diplomats at the UN in New York have said a peacekeeping mission might be approved by the Security Council later this week.

But the MoD says that, although the UK has offered to help, such assistance depends on many things and agreement is a long way off.

Meanwhile, the former Chief of the Defence Staff, Field Marshal Lord Carver, has died at the age of 86.

Drastic cuts

Michael Carver was commissioned into the Royal Tank Corps in 1935 and ended the war with a DSO and Bar as well as a Military Cross.

Over the next 25 years, he held senior staff appointments in East Africa, Cyprus and the Far East.

He served as chief of the defence staff between 1973 and 1976, during which he attracted controversy with his drastic cutting-back of the Territorial Army.

Field Marshal Lord Carver was also the author of a number of books about military history.