The prime minister has told British troops in Iraq they must "win the peace" as well as the war.

Tony Blair flew unannounced to the southern Iraqi city of Basra on Sunday following a family break in Egypt.

Upon arrival he was briefed by senior military officials on peacekeeping and reconstruction progress.

He then addressed troops in the town liberated by UK forces and now under British control, saying the controversial war was in a "noble and good cause".

Praising the role of the military, Blair said British troops were the "new pioneers of soldiering in the 21st century".

"I don't think the reputation of the British armed forces has ever been higher than it is today or its prestige any greater," he said.

"As you know there are a few different opinions about the wisdom of conflict, but whatever opinions people have of that, there is absolutely nobody back home who has anything other than enormous pride in the British armed forces and rightly so.

"The threat that we face today, the threat our country faces and other countries across the world, is not the one that certainly my generation grew up with, it is not the prospect of a big world war where countries are fighting each other, you can never discount that but it is highly improbable.

"Except I suppose in one set of circumstances and those are the circumstances of chaos and that chaos comes today from terrorism, from a particular virus of Islamic extremism that is a perversion of the true faith of Islam but is nonetheless incredibly dangerous and which you see literally in every part of the world."

Blair added that "the other threat is brutal and repressive states which are developing weapons that can cause destruction on a massive scale and are a huge liability for the whole security of the world".

"Those two threats come together," he continued. "Democracies don't sponsor terrorism. No country that obeys the rule of law tortures and maims its citizens, no government that owes its position to the will of the people will spend billions of pounds on nuclear weapons whilst their people live in poverty.

"And these threats together produce chaos, because in the world in which we live if there is chaos, then the whole world system economically and politically breaks down.

"This conflict here was a conflict of enormous importance because Iraq was the test case of that.

"Iraq was a country whose regime had a proven record of the use of weapons of mass destruction, not just their development, and a regime so abhorrent, as you will now know better than you did before, literally hundreds of thousands of its citizens died in prison camps, in the ways of torture and repression.

"If we had backed away from that we would never have been able to confront this threat in the other countries where it exists."

Moving on to the reconstruction of the country, the prime minister told troops winning the peace was as important as winning the war.

"But there is one reason why I think we can be optimistic," he said. "It is not just that the interests of ourselves and the Iraqi people are the same.

"What the Iraqi people want is prosperity, security, they want to bring up their families in some peace and decent way of living. And that is what we are trying to do. And that is the greatest challenge we face.

"Your soldiering has got not just to be about fighting and being able to engage in combat and win that combat and win it well which you do brilliantly, but also to win the peace, to win the hearts and minds of people. That work, again, you do brilliantly

"Iraq today is taking shape under your help and with your guidance in a way that would have been unthinkable a year ago. It is important to know that the work you have been doing is in a noble and a good cause.

"In years to come, people here in this country and I believe around the world will look back on what you have done and give thanks and recognise that they owe you a tremendous debt of gratitude and from the bottom of my heart I thank you very much indeed."

Blair later met local Iraqi leaders and US head of the Coalition Provisional Authority Paul Bremer along with Sir Jeremy Greenstock, the UK special envoy to Iraq.

His trip was the first he has made to the region since May and follows the capture of deposed Iraqi leader Saddam Hussein last month.

The visit comes ahead of the release of Lord Hutton's report into aspects of the justification for war.

Liberal Democrat leader Charles Kennedy said: "It is proper and fitting for the prime minister to pay personal tribute on behalf of us all to the skill and professionalism being shown by British forces in Iraq.

"They represent democracy in a country that was tyrannised.

"But after Lord Hutton's report, the democratic debate at home over the basis on which we went to war must, equally, be fully re-engaged."