UN nuclear watchdog chief Mohammed ElBaradei has said North Korea could possess several nuclear bombs.
ElBaradei wants Pyongyang to return to the negotiating table
Speaking on US television, he said Pyongyang had enough plutonium to make five or six nuclear weapons.
The country also has the necessary infrastructure to convert the plutonium into weapons, Mr ElBaradei added.
North Korea announced in February that it had nuclear arms - but that claim has not been verified by Mr ElBaradei's International Atomic Energy Agency.
When asked by CNN if it was the IAEA's assessment that North Korea already had as many as six bombs, Mr ElBaradei replied: "I think that would be close to our estimation."
"We knew they had the plutonium that could be converted into five or six North Korea weapons," he went on to say.
"We know that they had the industrial infrastructure to weaponise this plutonium. We have read also that they have the delivery system."
IAEA spokeswoman Melissa Fleming told the BBC there was no way the agency could know for sure whether North Korea had six bombs.
But she said it would not be surprising if it did.
'Cry for help'
The agency's inspectors were kicked out of North Korea at the end of 2002.
Pyongyang has shunned multilateral talks on its nuclear programme for almost a year.
Recently, reports have suggested it is preparing to test a nuclear bomb. Mr ElBaradei warned that a nuclear test would have disastrous political and environmental consequences.
"I do hope that the North Koreans would absolutely reconsider such a reckless, reckless step," he told CNN.
He said that whether the activity observed by satellites was real or simply a bluff, "it involves crying for help, frankly."
"North Korea, I think, has been seeking a dialogue with the United States, with the rest of the international community... through their usual policy of nuclear blackmail, nuclear brinkmanship, to force the other parties to engage them," he said.
Mr ElBaradei has already urged the international community to put pressure on North Korea not to go ahead with the test, and appealed to Pyongyang to return to the negotiating table.