North Korea may have one more uranium enrichment facility besides the existing facility located in the Yongbyon nuclear complex, a prominent U.S. nuclear scientist said Sunday.

David Albright, a physicist and head of the non-profit Institute for Science and International Security (ISIS), said North Koreans would not "put everything at Yongbyon," given the number of years they spent developing nuclear weapons.

He said the secretive communist nation may be preparing for another nuclear test, albeit not in a near future, and if so, it is expected to be based on both uranium and plutonium.

North Korea would need to boost missile explosive yield for the miniaturization of nuclear warhead, and a simple way to do it is to "build bigger core using plutonium and uranium together," Albright told Yonhap News Agency.

A possible scenario would be to put plutonium in the center and weapons-grade uranium outside in order to increase explosive yield, he said.

North Korea carried out plutonium-based nuclear tests in 2006 and 2009. It remains unconfirmed whether Pyongyang used uranium for its third-known nuclear experiment early this year.

For now, North Korea's uranium enrichment program is one of the biggest hurdles in efforts to restart the six-way talks, also involving South Korea, China, Russia and Japan, he pointed out.

But the Obama administration appears unwilling to invest as much time and energy in negotiations with North Korea as it does in talking with Iran, Albright said. (Yonhap news)