"I confirm this, though I do so with bitterness," Yushchenko, who will make an official visit to Washington next week, told NBC.

He said the X-55 missiles were exported under a forged contract that had Russia as the country of destination, but did not say when the sale took place.

A copy of the contract obtained by NBC appeared to bear clearance stamps for the export of 20 missiles to the Russia, which has denied any role in the sale, NBC said.

No nuclear warheads were sold with the missiles, made in 1987 which have a range roughly of 3,200 kilometers (2,000 miles) and were poorly maintained, according to a Ukranian source familiar with the investigation.

US intelligence officials quoted by NBC said China and Iran each obtained six missiles. Ukrainian officials have offered conflicting accounts of the number of rockets delivered.

Despite lacking nuclear warheads, the rockets could advance Iran's alleged quest for nuclear weapons -- they could reverse engineer the missiles, and double the range of its most powerful rocket, the Shahab-3, US intelligence officials told NBC.

Yushchenko is due to meet with President George W. Bush at the White House on Monday, and will address a joint session of the US Congress on Wednesday, during his visit to Washington that ends April 7.

The pro-Western Yushchenko defeated his pro-Russian rival Viktor Yanukovich in rerun presidential elections in December, which followed a popular uprising sparked by two previous fraudulent rounds of elections.