UN inspectors have discovered that equipment made in Japan, the arch-enemy of North Korea, has been used for uranium enrichment in the communist state, news reports said Thursday.

Police raided two private companies earlier this month after receiving the information from the International Atomic Energy Agency (IAEA), public broadcaster NHK and other Japanese media reported.

Police declined to comment on the reports, but one of the companies stepped forward to deny any wrongdoing.

Tokyo Vacuum, based in Kanagawa prefecture near the capital, and Tokyo-based trade agency Nakano Corp. are suspected of exporting vacuum pumps without permission to Taiwan, violating Japan's trade control law, the reports said.

Inspectors believe that the vacuum pumps, which can be used to separate uranium, were then sent to North Korea, which tested an atom bomb in 2006.

Nakano Corp. president Hiroshi Nakano told reporters that the company had received an order from Taiwan for the product and "simply responded."

"I had no idea the Taiwanese maker had that kind of relationship" with North Korea, he said. "If I had known about it, I would not have exported it."

Tokyo Vacuum was not immediately available for comment.

IAEA inspectors discovered the vacuum pumps when probing North Korea's Yongbyon nuclear complex and other nuclear-related facilities last July, media said.

The inspection took place to verify the shutting down and sealing of the nuclear facilities as it was agreed under the six-party disarmament deal on Pyongyang's nuclear programme.

Nakano Corp. shipped 10 vacuum pumps, which also have civilian uses, to a trading company in Taipei for a total of 500,000 yen (4,700 dollars) in summer 2003, the Yomiuri Shimbun reported.