North Korea may be adding seven nuclear bombs to its arsenal annually and could have about 20 bombs by the end of 2016, according to a U.S. analyst.

Siegfried S. Hecker, a nuclear weapons expert at Stanford University who has visited North Korea’s nuclear facilities as recently as 2010, states on 38 North, a Johns Hopkins University website dedicated to North Korea, that Pyongyang could add 330 pounds of highly enriched uranium to an existing stockpile of about 660 to 880 pounds.

That amount, 330 pounds, is sufficient to produce six nuclear bombs, according to Hecker.

While North Korea’s highly enriched uranium program is growing, the country’s capacity to produce plutonium “remains limited” to 13 pounds per year.

North Korea has about 70 to 120 pounds of plutonium that is worth six to eight bombs, the analyst writes, adding plutonium production is easier to track because of “telltale signals.”

Hecker also states that while North Korea has claimed it can produce lighter smaller warheads, its “ability to field an [intercontinental ballistic missile] is still a long way off – perhaps 5 to 10 years.”

North Korea’s universally condemned fifth nuclear test is raising concerns the country could conduct at least another test before the end of 2016.

Jin Xiangdong, a Chinese researcher at Xiamen University, told Sputnik News North Korea could soon launch a sixth nuclear test.