The Conservative leader has pledged to back Tony Blair as the country prepares for a possible war with Iraq.

Addressing the party's Spring conference in Harrogate, Iain Duncan Smith said he would support the prime minister as he "does the right thing".

He said the Conservatives would not engage in "political games" over the crisis, stressing that the national interest must come first.

But with some party members and senior MPs uneasy at his backing for any military action, Duncan Smith said there would be "no blank cheques" for the prime minister.

Making an emergency address as the conference began, the Tory leader told party members it had been a "difficult decision" to back the government.

"When the prime minister does something that is right, when he does something that I believe will benefit the British people and help bring peace to this part of the region, I believe, notwithstanding our other concerns, it is in the British interest for us to support him if he does what is right for Britain," he said.

"If people want me to play political games with this, I say I'm sorry I will not do it."

Making the case for possible military action, he warned of the threat to Britain posed by Iraq's weapons of mass destruction.

"Please do not pretend that we are not a potential target, for I believe we are," he said. "If anyone thinks otherwise, I am sorry, but we are living in cloud cuckoo land."

Duncan Smith also rejected suggestions that Iraq was too far away to pose a threat to the UK.

"This is not a far and distant country. This world is too small for us to turn our backs on people who may suffer or people who may cause that suffering. We as a party must be there and standing tall, and that is right."

Also addressing the conference, shadow foreign secretary Michael Ancram attacked the Liberal Democrats for saying they would back British troops while opposing any war.

"Charles Kennedy is hostile to Saddam at one moment, sympathetic at another," said Ancram.

"For the UN route last September, against the UN route in February, back in favour of it now. Against military action yesterday, apparently morally supporting it to day. What will his position be tomorrow?"

And shadow international development secretary Caroline Spelman joined the attack.

She accused the Lib Dems of "facing both ways on this issue". "Never mind serially reckless, this is seriously opportunist."