North Korea is presumed to be capable of building up to 79 nuclear devices by the end of 2020 as it has made strides in its weapons and missile programs, a South Korean expert said Tuesday.

Lee Sang-hyun, vice president at the research planning division of the Sejong Institute, told a forum that Pyongyang appears to be able to build four to eight miniaturized nuclear weapons annually.

His assessment was based on the assumption that the North currently has a maximum of 50 kilograms of plutonium and 300 kilograms of highly enriched uranium, according to his report prepared for the forum hosted by the Presidential Committee for Unification Preparation.

North Korea conducted its fourth nuclear test in January and fifth in September in defiance of international warnings and stiff sanctions.

It also test-fired more than 20 ballistic missiles, including the mid-range Musudan missile, which theoretically is capable of flying as far as the US territory of Guam.

Pyongyang is thought to be working on a nuclear-tipped intercontinental ballistic missile that can hit the US mainland.

In September, the country conducted a ground test for a new high-powered rocket engine, sparking speculation that it is moving closer to the goal.

North Korean leader Kim Jong-un has vowed to "permanently" defend the pursuit of developing nuclear weapons in tandem with boosting the country's moribund economy, commonly known as the "byeongjin" policy.

Lee said that the repressive regime is expected to stick to the "byeongjin" policy, adding that North Korea is not likely to change its behavior in the near term.

"Along with sanctions and pressure, there is the need to consider pursuing strategic persuasion and offering incentives in dealing with the North," the report showed. (Yonhap)