Mr Feith left the Pentagon in 2005

As under secretary of defence until 2005 Douglas Feith was closely involved with the planning of the invasion.

However, in "War and Decision", he blames officials outside the Pentagon for seriously mismanaging the invasion and occupation, the Post reports.

Out next month, it is the first insider account of Pentagon decision-making.

The newspaper says that Mr Feith accuses intelligence officials and the US state department, led at the time by Mr Powell, of repeatedly scuppering defence department plans for the invasion.

According to the Post, Mr Feith claims that US President George W Bush told a National Security Council meeting "war is inevitable" weeks before a team of UN weapons inspectors, headed by Hans Blix, had made their final report on Saddam Hussein's weapons capabilities.

'More harm than good'

Mr Feith reportedly singles Mr Powell out for criticism, saying that though he allowed himself to be portrayed as a dove, he never spoke out against the war.

He also criticises Condoleezza Rice, who took over from Mr Powell as secretary of state, for having failed in her then role as national security adviser, saying that she did not unite the US's war planning, the Post says.

And, according to the paper, he castigates Paul Bremer, the US official in charge of the subsequent US occupancy as having done more harm in Iraq than good and says military chief Gen Tommy Franks had no interest in post-war planning.

In stark contrast, Mr Feith is reportedly full of praise for former defence secretary Donald H Rumsfeld - one of the chief architects of the war.

Mr Feith was investigated by the Pentagon's inspector general last year for his department's pre-war assessments which linked Saddam Hussein's regime to the al-Qaeda terror group.

The assessments were judged "inappropriate" but not illegal.