UNITED NATIONS -- A former Russian top spy says his agents helped the government steal nearly $500 million from the UN'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, says he oversaw an operation that helped Hussein's regime manipulate the price of Iraqi oil sold under the program -- allowing Russia to skim profits.

Tretyakov, former deputy head of intelligence at Russia's UN 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 UN 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.

Tretyakov, 51, 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 UN, during an interview this week. "Inside the UN, we were fishing for knowledgeable diplomats who could give us, first of all, anti-American information."

His defection was first reported in 2001, followed by the news that he was not a diplomat, but a top Russian spy who was extensively debriefed by the CIA and the FBI.