North Korea said on Sunday that Japan's nuclear ambitions "must be prevented at any cost", after a Tokyo official reportedly suggested the country should possess atomic weapons.
Pyongyang's reaction came after the unnamed official in the prime minister's office was quoted by Kyodo News on Thursday as saying: "I think we should possess nuclear weapons."
The official was reported to have been involved in devising Japan's security policy.
The Kyodo report also quoted the source as saying: "In the end, we can only rely on ourselves" when explaining the necessity.
Pyongyang said the remarks showed Tokyo was "openly revealing their ambition to possess nuclear weapons, going beyond the red line".
"Japan's attempt to go nuclear must be prevented at any cost as it will bring mankind a great disaster," the director of the Institute for Japan Studies under the North's foreign ministry said in a statement carried by official Korean Central News Agency on Sunday.
"This is not a misstatement or a reckless assertion, but clearly reflects Japan's long-cherished ambition for nuclear weaponization," said the North Korean official, who was not named.
The official added that if Japan acquired nuclear weapons, "Asian countries will suffer a horrible nuclear disaster and mankind will face a great disaster".
The statement did not address Pyongyang's own nuclear program, which includes an atomic test first carried out in 2006 in violation of UN resolutions.
North Korea is believed to possess dozens of nuclear warheads and has repeatedly vowed to keep them despite a raft of international sanctions, saying it needs them to deter perceived military threats from the United States and its allies.
In an address to the United Nations in September, Pyongyang's vice foreign minister Kim Son Gyong said his country would never surrender its nuclear weapons.
"We will never give up nuclear power which is our state law, national policy and sovereign power as well as the right to existence. Under any circumstances, we will never walk away from this position," he said.
North Korean leader Kim Jong Un has also said he is open to talks with Washington, provided Pyongyang is allowed to keep its nuclear arsenal.
