North Korea has been restoring this week its main nuclear facility in Yongbyon, the Japanese daily Yomiuri Shimbun said Sunday.

The daily quoted a top U.S. official as saying Pyongyang began to reassemble the reprocessing facility two to three days ago to restart operations in two months. He also cited spent fuel rods at the Yongbyon site.

The official said that once the North resumes nuclear reprocessing, the volume of weapons grade plutonium could increase there.

He said North Korean leader Kim Jong-il could have ordered those steps with the United States in mind before he came down with illness.