The Carnegie Endowment for International Peace said in a report the United States also misrepresented the findings of UN weapons inspectors in a bid to strengthen its push for military action against Iraq last year.

Bush used Iraq's nuclear, chemical and biological weapons programmes and Saddam Hussein's ties to terrorism as the main case to the United Nations for its war against Iraq.

Several countries, led by France, Germany and Russia opposed the US-led war and the divisions have left deep diplomatic scars.

US Secretary of State Colin Powell admitted Thursday he had not seen "smoking gun concrete evidence" of Iraqi links with terrorism but insisted that Iraq was a threat that had to be dealt with.

Powell said he remained confident in the case against Iraq he put to the UN Security Council in a presentation on February 5 last year.

"I am confident of what I presented last year, the intelligence community is confident of the material they gave me," Powell told a press conference.

"I was representing them. It was information they presented to the Congress. It was information they had presented publicly and they stand behind it. And this game is still unfolding."

But the Carnegie foundation report entitled "WMD in Iraq: Evidence and Implications" said: "Administration officials systematically misrepresented the threat from Iraq's WMD and ballistic missile programmes."

It added that US intelligence "appears to have been unduly influenced by policymakers' views."

The foundation said the US government should enlist United Nations help to draw up "a complete history and inventory" of Iraq's WMD and missile programmes and establish an independent commission to establish what intelligence services knew about Iraqi weapons.

It said the United States should also revise its national security strategy allowing pre-emptive wars.

The 100-page report took six months to compile and examined claims made by the White House in the run up to the March 20 invasion that ousted former Iraqi dictator Saddam Hussein.

The Carnegie said the US administration misrepresented UN "inspectors' findings in ways that turned threats from minor to dire."

It said inspections by UN weapons experts "were on track to find what was there" and that international sanctions and import/export controls were "considerably" more effective than was thought.

The foundation said there was "no solid evidence" to back administration claims of a close relationship between Saddam and Osama bin Laden's al Qaeda network.

In launching the war, Bush had said Saddam's former government had presented a direct threat to the United States and the world.

The United States has failed to uncover any chemical, biological or nuclear weapons since the war. Hundreds of experts are still scouring Iraq in the hunt. But media reports have said the head of the US Iraqi Survey Group, David Kay, plans to stand down this year.

The foundation said there were at least two options "preferable to a war undertaken without international support."

The United States could have allowed inspections by the United Nations to continue until completed or imposed "a tougher programme of 'coercive inspections'."

The foundation said that on top of revising the national security policy to eliminate the possibility of more pre-emptive wars, the United States should also "make the security of poorly protected nuclear weapons and stockpiles of plutonium and highly enriched uranium a much higher priority."

Powell reaffirmed that the US administration believes it prepared a solid case against Iraq with the Central Intelligence Agency to present to other nations.

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