North Korea (search) may have enough weapons-grade plutonium (search) to make up to half a dozen nuclear bombs, the head of the U.N. atomic watchdog agency said in another warning about the reclusive regime's secretive nuclear program.

International Atomic Energy Agency (search) chief Mohamed ElBaradei told Cable News Network on Sunday evening that Pyongyang has the nuclear infrastructure to convert the material into atomic weapons.

"We knew they had the plutonium that could be converted into five or six North Korea weapons," ElBaradei told CNN.

Recent satellite imagery suggests North Korea may be preparing to test a weapon underground, and the IAEA has been urging the international community to increase pressure on Pyongyang to refrain from any such test.

IAEA inspectors were expelled from North Korea in 2002, and the agency has stressed that there is no way to know for sure whether the country is close to producing a nuclear weapon or is getting ready to test one.

ElBaradei described the latest developments as a "cry for help" on Pyongyang's part.

"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.

Last month, diplomats told The Associated Press that the United States was warning its allies that North Korea may be ready to carry out a nuclear test as early as June, basing the assessment in part on satellite photographs that suggested it was digging an underground test site.

The reported U.S. warnings reflected growing fears in Washington that the North is going ahead with efforts to develop nuclear weapons after South Korean officials said Pyongyang had recently shut down a reactor, possibly to harvest plutonium that could be used in an underground test.

The 5-megawatt reactor at Yongbyon generates spent fuel rods laced with plutonium, but they must be removed and reprocessed to extract the plutonium for use in an atomic weapon. They can be removed only if the reactor has been shut down.

The U.S. intelligence community believes North Korea has one or more nuclear weapons, and has untested two- and three-stage missiles capable of reaching U.S. soil. But it has been unclear whether Pyongyang has yet developed the technology to miniaturize a nuclear weapon so it fits on a missile, and provide it with the guidance systems so it can hit a target.