Five days into the war, Tony Blair has said "a huge amount has already been achieved" in Iraq.

As British and US troops near Baghdad, Blair predicted the "toughest fighting" was still to come.

The prime minister said the coalition's aim was "to remove Saddam as a means to removing his weapons of mass destruction".

Bringing the media up to date with military progress, Blair acknowledged that there were "pockets of pro-Saddam resistance" in Iraq.

But he vowed to overcome those still loyal to Saddam Hussein.

"They know that when the regime falls, which it will, they will have nowhere left to go," said the prime minister.

And he pledged to stand by the Iraqi people: "We will not let you down. Iraq will have a better future ahead of it."

Signalling that defeat was not an option, Blair said the "vast majority" of Iraqis wanted Saddam gone.

"The reason why I believe this will be won is not just the skill and professionalism of our armed forces but the fact that the cause is just," he said.

Addressing journalists inside Downing Street, Blair also warned that the scale of the humanitarian effort "is massive".

He said 16 million people were reliant on the oil-for-food programme.

Up to 400,000 children under five had died of malnutrition and disease over the last five years, he said.

Blair confirmed he will meet president Bush at Camp David.

The two leaders will discuss administration of post-war Iraq and the urgent need to clear the way for humanitarian aid.

The prime minister is also expected to press Bush to push ahead with the publication of the "road-map" for peace between Israel and Palestine.

On Thursday, Blair will head to New York where he will meet with secretary general Kofi Annan.

Whilst Blair conceded that "there may be some diplomatic difficulties" he expressed confidence that the UN would agree to plans for the post-conflict reconstruction of Iraq.

The prime minister said it was important to get a resolution on humanitarian assistance.

"I am confident we are going to be able to secure that," he said.

But he admitted there was still a "debate" on the shape of a post-Saddam administration.

Blair said the UK aim was to ensure the new governance structures were "endorsed" by the UN.

"The details of that we will discuss with the UN, with allies and others," he added.

"It is important that a post-Saddam Iraq is governed by a UN resolution."

But countries such as France, Germany and Russia - who opposed the military action - indicated that they do not wish to approve a resolution which legitimises the war.