Japanese government officials expressed regret Thursday over the reactivation of North Korea's nuclear facilities in Yongbyon and urged Pyongyang to end its provocation.
"It's regrettable," Prime Minister Junichiro Koizumi said. "We will call on North Korea to put an end to such action."
Japan will not play along with Pyongyang's recent attempts to draw attention to itself, Koizumi said.
"We will not be swayed by provocation," he said. "We'll take a calm and cautious stance."
Chief Cabinet Secretary Yasuo Fukuda meanwhile called the news "extremely regrettable," coming at a time when the world is working toward nuclear nonproliferation. The government has discussed the matter with the United States, he said.
The Yongbyon nuclear complex, located about 90 km north of Pyongyang, has a stockpile of 8,000 spent fuel rods that could be used to produce weapons-grade plutonium.
In December, North Korea removed seals on the reactor placed by the International Atomic Energy Agency.
Pyongyang said it would reactivate the complex to produce electricity after the U.S. stopped providing it with fuel oil in response to North Korea's resumption of its nuclear development program.