The fact that North Korea's weapons programme has been able to continue unabated is a legacy of the Cold War and, by and large, due to external influences, analysts said.
Dr Katsuhisa Furukawa, a former United Nations expert monitoring UN sanctions against the North, said: "Since the Cold War, North Korea has been known for its relatively impressive ability to reverse-engineer the foreign-sourced items and technologies, especially those from the former Soviet Union states."
This extends to building centrifuges and Pyongyang today is self-sufficient in its stockpile of uranium and plutonium reserves that are reportedly enough for at least 20 nuclear bombs.
It has conducted five nuclear tests thus far, including two last year. The fifth test last September produced a blast that, according some estimates, was more powerful than the atomic bomb that flattened Hiroshima in 1945.
Satellite images have shown that the North might be gearing up for a sixth test by excavating a tunnel at its test site that can withstand an explosive force up to 14 times more powerful than the previous test.
Analysts also said the North's apparent willy-nilly approach to testing missiles indicates that it has many more in its arsenal.
Experts have pointed out similarities between the intercontinental ballistic missile launched last week and the equipment used by Russia at the end of the Cold War.
Dr Furukawa said North Korea has been systematically collecting information and has developed advanced science and technologies from all over the world since the Cold War era - including scientists and engineers who have acquired advanced skills and expertise through their residence abroad.
It is unknown how many countries still receive researchers from North Korea today, he said. But at least until recent years, the North has "systematically dispatched researchers, scientists and students to foreign institutions in the fields relevant to nuclear and ballistic missile programmes, including in Russia, India, and Italy".
Dr Bong Young Shik from Yonsei University's Institute for North Korean Studies told The Straits Times that the basic model of North Korean missiles came from Iran, while the more recent technology hailed from China.
Security analyst Li Mingjiang from the S. Rajaratnam School of International Studies at Singapore's Nanyang Technological University, too, noted the close contacts that North Korea has with Iran and Pakistan.
While there has been no clear evidence to indicate so, Dr Narushige Michishita from the National Graduate Institute for Policy Studies in Tokyo said the rapid advancements suggest the outsize role of foreign influence. He said sympathisers from China and Russia were, perhaps, "the biggest suspects".