Pyongyang accused the United States on Tuesday of failing on its promise to remove North Korea from its list of state sponsors of terrorism and said it would immediately suspend disabling its nuclear facilities.
"The government of Japan is seriously concerned with the slowdown of the denuclearization process on the Korean peninsula," said Kazuo Kodama, a spokesman for the Foreign Ministry.
"Japan will continue applying pressure on North Korea in order to complete the dismantlement of the [Yongbyon] facility in close cooperation with all participants in the six-party talks," the diplomat said.
South Korea's foreign ministry called the North Korean move "regrettable."
The six-party talks on nuclear disarmament of the Korean peninsula, which comprise the two Koreas, China, Japan, Russia and the United States, have recently stalled.
North Korea insists it has met its denuclearization commitments in full, and is demanding that the United States end its "hostile policies."
Under deals reached last year, the reclusive Communist regime began disabling the reactor and other facilities at Yongbyon last November under U.S. supervision. Pyongyang says 80 percent of the work has been completed.
However, Washington insists that the North must accept strict procedures to verify the declaration it made in June of its nuclear activities before it can be taken off the blacklist.
The foreign ministers of the six countries involved in negotiations on North Korea's nuclear disarmament held a meeting in Singapore in late July and agreed to discuss a mechanism to verify the June declaration by Pyongyang on its weapons-grade plutonium stockpile.
