Japan lashed out Friday over North Korea's claim that it has finished reprocessing about 8,000 spent fuel rods and is using extracted plutonium to make nuclear weapons.
"What North Korea has done is regrettable, given the agreement at the six-nation talks not to escalate the situation," Deputy Chief Cabinet Secretary Masaaki Yamazaki told a regular news conference.
Foreign Minister Yoriko Kawaguchi made a similar comment at a separate news conference.
At the six-way talks in Beijing in late August, China, Japan, North and South Korea, Russia and the United States agreed not to make any moves that would worsen the situation surrounding Pyongyang's nuclear threat.
Yamazaki and Kawaguchi both said Japan has no concrete evidence to confirm the North Korean claim.
On Thursday, a North Korean Foreign Ministry spokesman said in a statement that Pyongyang would continue to reprocess spent fuel rods from the 5-mw reactor in the Yongbyon nuclear complex.