The UN has the international legitimacy to guide the handover of power in Iraq on 30 June despite a corruption probe, says UK Prime Minister Tony Blair.
Limited oil production was permitted during Saddam Hussein's rule
The UN Security Council has approved an investigation into reports of massive corruption in the UN-administered oil-for-food programme in Iraq.
The now defunct scheme was designed to help Iraq buy humanitarian goods and ease the impact of sanctions.
But the PM said he backed the UN role in Iraq despite its past.
An adviser to the Iraqi Governing Council told the BBC that the oil-for-food programme allowed Saddam Hussein to buy influence abroad.
He said the former Iraqi leader spent billions of dollars bribing foreign businesses, journalists and officials.
"The oil-for-food programme provided Saddam Hussein with a convenient vehicle through which he bought support internationally," Claude Hankes-Drielsma, a British adviser to the US-backed Governing Council, told the BBC's Today Programme.
Mr Hankes-Drielsma quoted a recent report by the US Treasury, estimating that $10bn of illicit gains were made from the oil-for-food scheme.
Mr Blair told reporters at his monthly Downing Street news conference it was important the UN was investigating the allegations and also to distinguish between what was happening now and in its past.
He said the process towards the handover of power being conducted by Lakhdar Brahimi, the UN's special envoy in Iraq, had a "broad basis of consent within the various groups in Iraq".
"Whatever difficulties there are historically about the UN's role in Iraq ... the UN is the body that has the international legitimacy to be able to certify and help guide the process of political transition," Mr Blair said.
"This is an extraordinary and crucial moment in Iraq's development - it is why so much fighting and terrorism is going on to stop it."
Mr Blair said it would be "a huge thing for everyone" if Iraq moved towards becoming a democracy by the end of 2005.
"The UN does have that sufficient legitimacy in Iraq as well as outside despite the past," he added.
The UN Security Council welcomed a wide-ranging inquiry proposed by UN Secretary General Kofi Annan and called for all governments to co-operate.
But Mr Hankes-Drielsma said some countries on the council had benefited from the bribes and were "part of the problem".
Launched in 1996, the oil-for-food programme was the largest humanitarian operation ever undertaken by the UN and was meant to help civilians.
Recent media reports have accused individuals and companies from more than 40 countries, including a senior UN official, of being involved in corruption and bribery in connection with the oil sales.
The former UN humanitarian coordinator in Iraq, Hans von Sponeck, said the allegations needed to be cleared up, but denied that the world body was closely involved in corruption.