United Nations ? A former Russian top spy says his agents helped the Russian government steal nearly $500 million from the U.N.’s oil-for-food program in Iraq before the fall of Saddam Hussein in 2003.

Sergei Tretyakov, who defected to the United States in 2000 as a double agent, says he oversaw an operation that helped Saddam’s regime manipulate the price of Iraqi oil sold under the program – and allow Russia to skim profits.

Tretyakov, former deputy head of intelligence at Russia’s U.N. mission from 1995 to 2000, names some names, but sticks mainly to code names. Among the spies he says he recruited for Russia were a Canadian nuclear weapons expert who became a U.N. nuclear verification expert in Vienna, a senior Russian official in the oil-for-food program and a former Soviet bloc ambassador. He describes a Russian businessman who got hold of a nuclear bomb, and kept it stored in a shed at his dacha outside Moscow.

The 51-year-old Tretyakov had never spoken out about his spying before this week, when he granted his first news media interviews to publicize a book published Thursday. Written by former Washington Post journalist Pete Earley, the book is titled “Comrade J.: The Untold Secrets of Russia’s Master Spy in America after the End of the Cold War.”

“It’s an international spy nest,” Tretyakov said of the U.N., during an interview this week with The Associated Press. “Inside the U.N., we were fishing for knowledgeable diplomats who could give us first of all anti-American information.”

His defection was first reported by the AP in 2001. Shortly after, the New York Times broke the news that he was not a diplomat, but a top Russian spy who was extensively debriefed by the CIA and the FBI.

Some of the people named or referenced by a code name in the book have denied Tretyakov’s claims. The Russian mission to the U.N. said Friday it would have no immediate comment.

Stephane Dujarric, a spokesman for U.N. Secretary-General Ban Ki-moon, described Tretyakov’s allegations as potentially serious violations of law and U.N. rules.

But Dujarric said it would be up to others to prosecute if the allegations are substantiated: “Since the U.N. can’t prosecute, it is now up to national governments to prosecute.”

An 18-month investigation into the oil-for-food corruption, led by former Federal Reserve chairman Paul Volcker, culminated in an October 2005 report accusing more than 2,200 companies from some 40 countries of colluding with Saddam’s regime to bilk the humanitarian program in Iraq of $1.8 billion.

The program was aimed at easing Iraqi suffering under U.N. sanctions imposed after Saddam’s 1990 invasion of Kuwait. It allowed Iraq to sell oil provided the bulk of the proceeds were used to buy food, medicine and other humanitarian goods and to pay war reparations. Volcker’s reports blamed shoddy U.N. management and the world’s most powerful nations for allowing corruption in the $64 billion program to go on for years.

Tretyakov defected to the United States with his wife and daughter in 2000, after serving as a double agent passing along secrets to the U.S. government. He calls his defection “the major failure of Russian intelligence in the United States” and warns that Russia, despite the end of the Cold War, harbors bad intentions toward the United States.