U.S. Ambassador Alexander Vershbow says North Korea should clear up suspicions on the centrifuges it purchased from Pakistan and its highly enriched uranium (HEU) program.

In a chat on the American Embassy’s Web community Café USA, Vershbow said Tuesday that the North’s purchase of the centrifuges was even confirmed in the memoirs of Pakistani President Pervez Musharraf.

The U.S. envoy said that Washington takes the HEU issue seriously, adding that its top nuclear envoy Christopher Hill also made it clear that Pyongyang must disclose its HEU program in line with February's six-party nuclear agreement.