The last major remnant of Saddam Hussein's nuclear program, a huge stockpile of concentrated natural uranium, reached Montreal on Saturday to complete a top-secret U.S. operation.

The removal of 550 metric tonnes of "yellowcake," the seed material for higher-grade nuclear enrichment, included a two-week airlift from Baghdad and a voyage across two oceans.

The Iraqi government sold the yellowcake to a Canadian uranium producer, Cameco Corp., in a transaction the official described as worth "tens of millions of dollars."

A Cameco spokesman, Lyle Krahn, said the yellowcake will be processed at facilities in Ontario for use in energy-producing reactors.

"We are pleased … that we have taken [the yellowcake] from a volatile region into a stable area to produce clean electricity," Krahn said.

U.S. and Iraqi forces have guarded the 9,300-hectare yellowcake site since its discovery.

The deal culminated more than a year of intense diplomatic and military initiatives — kept hushed in fear of ambushes or attacks once the convoys were under way.

It also brought relief to U.S. and Iraqi authorities who had worried the cache would reach insurgents or smugglers crossing to Iran to aid their nuclear ambitions.

Diplomats and military leaders first weighed the idea of shipping the yellowcake overland to Kuwait's port on the Persian Gulf.

Such a route, however, would pass through Iraq's Shiite heartland and be within easy range of extremists.

The ship also would need to clear the narrow Strait of Hormuz at the mouth of the Gulf, where U.S. and Iranian ships often come in close contact.

Kuwaiti authorities, too, were reluctant to open their borders to the shipment despite top-level lobbying from Washington.

Deal reached earlier this year

The yellowcake still needed a final destination. Iraqi government officials sought buyers on the commercial market, where uranium prices spiked at about $120 per pound last year. It's currently selling for about half that.

The Cameco deal was reached earlier this year, the official said.

At that point, U.S.-led crews began removing the yellowcake from the Saddam-era containers, some leaking or weakened by corrosion, and reloading the material into about 3,500 secure barrels.

In April, truck convoys started moving the yellowcake from Tuwaitha to Baghdad's international airport.

Then, for two weeks in May, it was ferried on 37 flights to Diego Garcia, a speck of British territory in the Indian Ocean where the U.S. military maintains a base.

On June 3, an American ship left the island for Montreal.

While yellowcake alone is not considered potent enough for a so-called "dirty bomb" — a conventional explosive that disperses radioactive material — it could stir widespread panic if incorporated in a blast.

Yellowcake also can be enriched for use in reactors and, at higher levels, nuclear weapons using sophisticated equipment.