Oil exports have dropped by 24%

Under oil-for-food, Iraq is allowed to export oil in exchange for food and medicine imports, to ease the effects of the crippling sanctions it has been under since 1990.

But Mr Sevan, who has just returned from Iraq, said the UN sanctions committee responsible for authorising imports had become politically paralysed.

He said a new retroactive pricing initiative, whereby the sanctions committee sets the price for Iraqi oil several weeks after it is sold, had caused a 35% drop in the country's crude oil exports since November.

This has diminished the amount of money available for the humanitarian programme.

'Major cracks'

Mr Sevan also attacked a continued US block on a series of contracts worth $5bn, which he has repeatedly asked to be lifted.

The contracts have been blocked while the United States, Britain, France, Russia and China, attempt to reconcile their differences over the future of the sanctions regime.

"One could say, without any hesitation, that the work of the committee is paralysed with numerous issues awaiting action for long periods of time," Mr Sevan said.

"We already are witnessing major cracks in our capacity to implement the programme effectively, with so many political and procedural hurdles," he said.