A nuclear North Korea is unacceptable: Obama

Maintaining that a nuclear North Korea is unacceptable, US President Barack Obama has asked Pyongyang to take concrete steps to abide by its international commitments and obligations.

"We're going to stand firm in our insistence that a nuclear North Korea is unacceptable," Obama said.

His comments came amid reports that North Korea may be preparing a fourth nuclear test.

"The burden is on Pyongyang to take concrete steps to abide by is commitments and obligations, and the United States, Japan and South Korea are united in our goal-the complete denuclearization of the Korean peninsula," he said in an interview to the popular Japanese newspaper Yomiuri Shimbun.

Obama is currently in Japan -- his fifth trip to Asia.

"I would add that, even as we face the nuclear threat from North Korea, we remain deeply concerned about the desperate plight of the people of North Korea as well as other humanitarian issues," Obama said.

"We will never stop working for the day when all the people of the Korean peninsula can live in security, peace and freedom," he said.

Obama said North Korea's nuclear and ballistic missile programmes are a threat to US allies Japan and South Korea, a threat to the region, and increasingly a direct threat to the security of the United States.

"In the past, the North thought its provocations could drive a wedge between our three countries. Instead, in recent years the United States, Japan and South Korea have stood united, deepened our trilateral cooperation and made it clear to Pyongyang that the days when its threats would elicit concessions are over. Today, North Korea is more isolated than ever," he said.