North Korea might be able to develop intercontinental ballistic missile capable of hitting the US mainland by 2020 at the latest, a South Korean think tank has said in its 2016 annual report.

The think tank also said that the reclusive state, led by Kim Jong-un, has already secured a technology to miniaturise nuclear warheads and load them onto its Scud and Nodong ballistic missiles to hit the US.

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"The North is estimated to have succeeded in developing nuclear warheads on par with boosted fission weapons through its fourth and fifth nuclear tests," the Institute for National Security Strategy under the National Intelligence Service said in its report released on Sunday (25 December).

The fifth nuclear test conducted by Pyongyang on 9 September was said to be the strongest so far. The blast, which also triggered a powerful earthquake, was measured at 10 to 20 kilotons, compared to the third test conducted in 2015 that measured 7.9 kilotons. The fourth test conducted in January this year measured 6 kilotons, Yonhap quoted the report as stating.

The seriousness of the North Korean nuclear programme lies in the rapid growth in the number of warheads, as well as its miniaturisation and diversification," the report noted, referring to the increasing power of the recent nuclear tests.

North Korea ballistic missile launch
South Korean think tank, the Institute for National Security Strategy under the National Intelligence Service, said North Korea would be able to develop intercontinental ballistic missile capable of reaching the US mainland by 2020 - File photo KCNA via Reuters

Commenting on the several missile tests conducted by North Korea, the report said: "Of the North's eight Musudan missile tests this year, all, excluding the sixth, ended in failure. In the sixth test, a Musudan missile went up over 1,000 kilometers before re-entering Earth's atmosphere and flying an additional 400 km."

According to the institute, North Korea will take several years to deploy submarine-launched ballistic missile SLBM. It has, however, cautioned that the deployment is now "a matter of time" and not technology. "Considering the capabilities of North Korean submarines, U.S. military bases not only in South Korea but in Japan will be under threat," the report said.

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