North Korea responded by warning of a "merciless retaliatory strike" if the USA acts first. But the United States media is reporting that there are indications of a North Korean nuclear test, and even security experts are drawing upon the analysis of satellite imagery to conclude that North Korea has completed preparations for a nuclear test.
Meanwhile, an American nuclear-powered aircraft carrier group has been dispatched to boost an array of military capabilities available to Washington in South Korea and the wider region.
"We can see from today that North Korea's missile technology has advanced far more than we had previously thought".
Han warned that North Korea has a "powerful nuclear deterrent" in hand and "will not keep our arms crossed in the face of a USA pre-emptive strike".
The North launched a ballistic missile from the same region earlier this month ahead of a summit meeting between the leaders of the United States and China, its key ally, to discuss the North's increasingly defiant arms programme.
The missiles were among one element of a massive, militaristic parade to mark the 1912 birthday of the regime's founder, Kim Il Sung.
Also on display was a powerful mid-range missile that outside analysts call a "Musudan", and which can potentially reach USA air bases in Guam, as well as a new solid-fuel mid-range missile that can be fired from land mobile launchers, making them harder to detect before launch.
The official, who wasn't authorised to be quoted by name and demanded anonymity, lamented Pyongyang's "far too common and far too dangerous" provocations, and said Washington would work with worldwide partners to cut the North's government off "from the rest of the world". North Korea also launched a long-range rocket past year that put a satellite into orbit, which Washington, Seoul and others saw as a banned test of missile technology.
State TV showed North Korea's Pukkuksong submarine-launched ballistic missiles (SLBM) on parade with tanks and other heavy machinery in front of Kim Jong Un.
A conflict over North Korea could break out "at any moment", China's Foreign Minister Wang Yi said yesterday, warning there would be "no winner" in any war as tensions soar with the United States.
"The U.S. missile attack against Syria is a clear and unforgivable act of aggression against a sovereign state, and we strongly condemn this", an unnamed spokesman was quoted by the agency.
The North has reiterated its constant refrain that it is ready for "war" with the US.