The lack of planning had plagued reconstruction since the US-led invasion, and been exacerbated by a “general lack of co-ordination” between US government agencies charged with the rebuilding of Iraq, said Stuart Bowen, the special inspector-general for Iraq reconstruction, in a report released on Sunday.

His 110-page quarterly report, delivered to Congress at the weekend, has underscored how a “reconstruction gap” is emerging that threatens to leave many projects planned by the US on the drawing board.

“Nearly two years ago, the US developed a reconstruction plan that specified a target number of projects that would be executed using the Iraq Relief and Reconstruction Fund.

“That number was revised downward [last year]. Now it appears that the actual number of projects completed will be even lower,” Mr Bowen says in his report.

Increasing security costs were “the most salient” reason behind the shortfall, he concluded.

While 93 per cent of the nearly $30bn (€25bn, £17bn) the US has appropriated for reconstruction has been committed to programmes and projects, more than 25 per cent of the funds have been spent on security costs related to the insurgency.

The largest expected increase in costs to complete planned projects had occurred in the Project and Contracting Office (PCO), which manages projects in the oil, electrical, security and water sectors and has been allocated $4.6bn in reconstruction funds.

While in most sectors PCO data indicated that project costs would not exceed initial estimates, Mr Bowen found that oil sector-related costs had been under-estimated by about $790m.

Conflicting data also showed “possible funding anomalies”, because although the PCO reported that more than 85 per cent of oil projects were on or ahead of schedule, other data showed that the cost of completing the tasks was increasing beyond initial estimates.

The report said a separate agency given the job of assisting the Iraqi government in training and equipping security forces – a job for which it was allocated $835m – had spent 14 per cent more than originally estimated.

The special inspector-general also highlighted a stark increase in non-military deaths in connection to Iraq’s reconstruction. The number of non-Iraqi contractor deaths from all countries rose to 412 for the period of March 2003 to September 2005. That compared to 120 deaths up until Sptember last year.

While the most successful post-conflict reconstruction effort in US history – the reconstruction of Japan and Germany following the second world war – began being planned in the months after the US entered the war, Mr Bowen found that “systematic planning” for the post-hostilities period in Iraq was “insufficient in both scope and implementation”.