Iraq and likeminded nations should not be overlooked in the war against terrorism, Iain Duncan Smith warned on Thursday.

Speaking in Washington on his first trip abroad since becoming party leader, he supported President Bush's warning to Saddam Hussein on weapons inspectors.

In an interview on the BBC Radio 4 Today programme, he said: "I think now is the time for us all to stay together and resolve that we won't let countries like Iraq off the hook and ensure that we can inspect and get rid of their weapons of mass destruction.

"In the last three years countries like Iraq - and there are others too - have used that period to build up some very nasty weapons of mass destruction and are prepared and willing to use them. We have to ask ourselves at what point do we insist that these weapons must be dismantled. We started and we haven't finished".

His comments echoed those of defence secretary, Geoff Hoon, who pledged British support for the war's continuation while giving evidence to the defence select committee.

Duncan Smith denied that extension of the war from Afghanistan would place too much pressure on the coalition. He said: "So long as there is a clear sense that we have the right country and that we are making just and reasonable demands, I think the coalition will hold together.

"Politically we must maintain our resolve that this didn't begin and end with Afghanistan because to do that is simply to walk away having cured only one part of the illness. There must be clear evidence of connection to these acts. My point is that once we have established that sort of evidence of various acts then we do need to show that resolution and act."

However, the German chancellor, Gerhard Schroder, has warned that many European countries would not support such a move." We should be particularly careful about a discussion about new targets in the Middle East - more could blow up in our faces there than any of us realise," he said.

Criticisms

Duncan Smith's warning was criticised by the Iraqi representative in the UK, Dr Mudhafar Amin, who dismissed the intervention as "party politics".

"If anybody is sincere in solving the problem this is not the approach: putting Iraq in a corner, demonising it and hitting it - and you expect us to co-operate in a very nice and gentle way? If they are really sincere, they should use a diplomatic approach, they should use dialogue, they should use the United Nations," said Amin.

A spokesman for the Campaign for Nuclear Disarmament said: "Obviously he is trying to have a position that is different to the government. But if you look at Geoff Hoon's comments...the government is not that far behind. We're concerned that the leader of the opposition should be in Washington talking to some pretty hawkish people in the US administration. We are very concerned and are closely monitoring the situation."

Liberal Democrat foreign affairs spokesman Menzies Campbell said: "Loose talk about extending military action to Iraq will undermine the coalition against terrorism particularly in Arab capitals throughout the Middle East. Unless there is incontrovertible evidence of Iraqi involvement in terrorist activity no Arab government could possibly support the United States in military action."

"Saddam Hussein would be bound to try to draw Israel into the conflict by launching missiles at Tel Aviv as he did during the Gulf War. Israel showed great self-restraint at that time, but in the present circumstances it would be impossible to guarantee that Israel would not feel compelled to retaliate."

During his visit, Duncan Smith will speak at a conference organised by the American Enterprise Institute and will meet members of the Bush administration including vice president Dick Cheney and national security adviser, Condoleezza Rice.

In a visit to New York, he will meet the city's outgoing mayor Rudolph Guiliani and see the site at ground zero. He will also have discussions with the state governor, George Pataki.