U.S. Scientist Who Has Seen N Korea's Nuclear Secrets Says White House Should Be Concerned

US scientist has seen North Korea's nuclear secrets

An American scientist who has seen the North Korean nuclear secrets claims Kim Jong-un is not bluffing and that the White House should be concerned. 

Dr Sig Hecker, who was once in charge of designing nuclear weapons for the US, was shown around the hermit kingdom seven times and each time was given access to confidential information.

The doctor, who the North Koreans knew would feed the information back to his bosses in America, held plutonium extracted at a secret complex in Yongbyon. 

Combined with the country's massive stock of uranium, it is estimated Kim Jong-un's army has between 30 and 60 nuclear weapons at its disposal, according to Hecker. 

Experts now believe Pyongyang has a better understanding of Washington than the other way around, which could be a stumbling block for Donald Trump.  

Hecker told CBS: 'I was immensely surprised by how much they showed me and with the openness with which they showed and explained that to me.'

He had been director of the Los Alamos National Laboratory - more commonly known as the birthplace of the American atomic bomb - for 11 years.

In 2004, he was invited for his first tour of Yongbyon, and he has returned six times since. 

It was here he was given North Korean plutonium to hold - a heavy, radioactive metal encased in a glass jar. 

The moment Hecker physically testified to the isolated nation's nuclear might, the balance in Washington shifted. 

'It changed from one of "we don't know exactly what they have, if they have enough to make anything" to the fact that they actually could have four to six bombs,' he said.

The complex continues to be monitored by satellites orbiting above the country, and 14 years later it is thought the number of weapons has increased by at least five-fold. 

Expert Robert Carlin, who has been studying North Korea for four decades, told CBS: 'I think they understand us better than we understand them. We're still weighed down with a lot of stereotypes and they're going to trip us up.'

By now, the building which Hecker was given access to has doubled in size meaning it could be holding up to 10,000 centrifuges, according to director of the Institute for Science and International Security David Albright. 

Given the rate of development, he estimates North Korea has 13 to 30 nuclear weapons. 

Hecker believes this figure could be as high as 60, and that more worrying was the fact that they could be built as small disco-ball-type bombs, capable of being fitted to a missile.