The Washington Post says the United States has obtained intelligence suggesting that North Korea might have produced highly enriched uranium under an alternative route for producing a nuclear weapon.

The U.S. daily reported Saturday that according to sources familiar with the intelligence, Washington has discovered fresh traces of highly enriched uranium while examining 18,000 pages of North Korean documents.

Pyongyang provided the documents that date back to 1987 to help Washington verify the volume of plutonium it produced in the Yongbyon reactor.

The North has denied the existence of the uranium program, and its upcoming nuclear declaration is expected to show that the Yongbyon reactor produced about 37 kilograms of plutonium.