North Korea conducted a nuclear test on Monday and later test-fired three additional short-range missiles within a range of 160 km from Musudanri, North Hamgyong Province and Wonsan area. The test has sparked fresh speculation about its military capacity.

The first purported nuclear test in 2006 left some skeptical  whether the North really had a properly functioning nuclear weapons system based on an estimated explosive force equal to less than 1,000 tons of TNT.

But now doubts are disappearing, with the test this time suggesting a nuclear weapon with 10 times stronger explosive force. Experts speculate the North has managed to improve the nuclear trigger device.

It is worth noting that North Korea has already tested a long-range ballistic missile twice, and missiles are the most powerful means of delivery of nuclear weapons.

There is now speculation that the North may have produced nuclear warheads that could be carried by a Scud missile, which has a range of 300 to 500 km, or a Rodong, which has a range of 1,300 km, since both can carry heavier warheads than long-range ballistic rockets. North Korea has some 600 Scuds and some 200 Rodongs.

A researcher with a government-funded think tank who asked to remain anonymous said, "If it succeeds in putting a nuclear warhead on an intercontinental ballistic missile, the North would be ranked among a club of nuclear states including China and India. That would cause a great stir in the international community."