"It's time for UN Secretary General Kofi Annan to resign," Republican Senator Norm Coleman, chairman of the Senate investigations subcommittee, wrote in the article to be published Wednesday.

"I have arrived at this conclusion because the most extensive fraud in the history of the UN occurred on his watch," the Minnesota senator wrote.

He added that "as long as Mr. Annan remains in charge, the world will never be able to learn the full extent of the bribes, kickbacks and under-the-table payments that took place under the UN's collective nose."

The oil-for-food program, launched in December 1996 and terminated in November 2003, was intended to allow Iraq to sell oil under UN supervision to buy food and humanitarian supplies, and eventually developed into the largest aid scheme in UN history.

But US congressional investigators say Saddam's regime may have skimmed billions of dollars from the program, and allegations have surfaced of pay-offs to officials and private individuals from around the globe.