North Korean leader Kim Jong-un has visits a nuclear-material production base in this undated photo provided by the North's Central News Agency on Jan. 29. Yonhap

North Korean leader Kim Jong-un has inspected a nuclear-material production base and a nuclear weapons institute, emphasizing that strengthening his country's nuclear shield was "indispensable" amid a long-term confrontation with "the most vicious hostile countries."

Kim made the remarks during his inspection of the production base and the Nuclear Weapons Institute, where he reviewed the core processes for producing weapons-grade nuclear materials and learned about the present production status, the Korean Central News Agency (KCNA) said Wednesday, without specifying the date.

North Korea's security situation, in which "a long-term confrontation with the most vicious hostile countries is inevitable," makes it "indispensable" for the country to steadily strengthen the nuclear shield to cope with existing and new security dangers and to guarantee its sovereignty, interests and development right, the KCNA quoted Kim as saying.

The external situation facing North Korea "remains grave and the challenges of the hostile forces are becoming ever more pronounced," he said, adding that nuclear weapons stockpiling and its increase by geometrical progression provide an absolute force capable of thoroughly containing North Korea's enemies.

The leader stated the country's nuclear technical forces are growing stronger day by day, affirming that "guaranteeing peace and security by dint of strength is our mode of struggle and option."

He also ordered the overfulfillment of the plan for producing weapons-grade nuclear materials and the strengthening of the country's nuclear shield.

The KCNA did not specify the nuclear-material production base Kim visited, but photos it published suggest it might be the same facility he inspected in September last year.

Reporting to the National Assembly last year, South Korea's spy agency said the facility was likely to be the Kangson nuclear complex near Pyongyang, which is one of the two known nuclear facilities operated by the reclusive state, along with the Yongbyon nuclear site.

Some observers also raise the possibility that the production base visited by Kim this time could be a different complex.

"It is possible to install a uranium enrichment facility within a short period, and the facility shown in the reported photo appears more outdated than the one revealed in September last year," Hong Min, a senior research fellow at the Korea Institute for National Unification, said, suggesting it may be Yongbyon or a different facility.

Kim's latest pledge for stronger nuclear capabilities, coming just days after U.S. President Donald Trump expressed an intent to reach out to him, suggests he may not reciprocate and instead continue with the current confrontational stance. (Yonhap)