Speaking at the Center for Disarmament and Non-Proliferation in Vienna on Thursday, a prominent US expert downplayed any North Korean threat.

North Korea has unleashed a torrent of rhetoric in recent weeks, pushing the Korean peninsula closer to the brink of a nuclear war. But what seems to be an endless tirade could just as well be an empty threat, said nuclear scientist Siegfried Hecker.

“All of these things that they have threatened to do, most of them they cannot do,” said Hecker, who has visited the North’s nuclear facilities several times. He also revealed the existence of a uranium enrichment facility in the isolated nation.

Currently, he said, North Korea has “not much” plutonium, enough for four to eight weapons, and would take much longer to produce more even if it were to restart its main Yongbyon nuclear complex.

“So the world does not have to be concerned that when they made that decision to restart that reactor, that tomorrow they would have more bombs. They can’t have more bombs tomorrow,” he said.

Resuming operations at Yongbyon would take six months and around three years would be required until it could produce plutonium, he added.

Moreover, the North is still some distance from having a nuclear warhead on a missile and was “at least five years” away from having a missile capable of reaching the US.

“The bark is much greater than the bite,” he said. “But you still have worry about it. It is a serious situation”.

North Korea has laid out pre-conditions for Washington and Seoul if they want to press ahead with talks but South Korea made no sign of relenting to Pyongyang’s demands.