Missile components companies in Russia and Uzbekistan are cooperating in the sales of parts to Stalinist North Korea, which has pledged to the US it will stick to a moratorium on missile testing, the Washington Times reported.

Parts being sold included the aluminium alloys, laser gyroscopes and missile guidance systems, the report said, adding that the information was contained in a sensitive intelligence reports sent to senior policymakers.

The report also said Russia was collaborating with a North Korean missile company to send Scud missiles to Yemen.

US officials are due to meet North Korean counterparts in Kuala Lumpur next month for a new round of talks on Pyongyang's missile program and alleged proliferation activities.

President Bill Clinton warned on Thursday that despite signs of reconciliation that emerged from a summit this month between North Korea and South Korea, Pyongyang's weapons program remained a threat.

The report also quoted a National Security Agency assessment on June 8, which found that Russia had exported tritium gas to a nuclear weapons research centre in Iran.

Tritium is sometimes used to enhance the explosive power of nuclear warheads.