TOKYO - When North Korea fired the intermediate-range Hwasong-12 ballistic missile over northern Japan less than three weeks ago, Prime Minister Shinzo Abe called it "unprecedented, serious and significant threat".

Returning from a widely successful visit to India on Friday (Sept 15) morning, he told reporters at the Haneda Airport that the second missile lobbied over Hokkaido hours earlier was "unacceptable".

Tokyo, he said, can "never tolerate" North Korea's "dangerous provocative action that threatens world peace". Other top Japanese officials made similar remarks.

The seemingly trite response of the Japanese government, however, shows up Tokyo's predicament in dealing with North Korea, which makes no secret of its desire to inflict maximum damage on its former colonial ruler.

On the eve of its latest missile launch, it had threatened to sink Japan with a nuclear weapon in retaliation against Tokyo's support of the strongest-ever set of UN sanctions imposed on North Korea.

"Japan no longer needs to exist near us", the Korea Asia-Pacific Peace Committee, which handles the North's external ties and propaganda, said in a statement carried by the North's official KCNA news agency.

Kobe University defence expert Tosh Minohara told The Straits Times that North Korea has constantly been threatening Japan because it knows there will be minimal consequences.

"North Korea sees Japan as the weakest power in the region. Kim Jong Un has been very careful not to directly target (its missiles at) Hawaii or Guam because the US will react to that. But what Mr Abe said today is a catchphrase that has been used over and over again," he said.

"We've heard this many times, but it's so passive, and it's not like the North's actions will bring forth great consequences. The risk of blowback is minimal and you can almost predict how Japan will react," he added, noting that the "almost scripted" reaction is "all bark but no bite".

Japan is clearly caught in a Catch-22 situation.

While it needs to arm itself with conventional offensive weapons to avoid being seen as a "pushover", Mr Abe's attempts to rewrite the Pacifist Constitution and to beef up Japan's defences have resulted in political blowback from China and South Korea, where wounds from Japan's wartime aggression still rankle.

"The cycle has to be broken," Dr Minohara said.

"Time favours the DPRK regime and doesn't favour us," he said, using the North's official name of Democratic People's Republic of Korea.

With each test, North Korea has improved on its missile capabilities.

Friday's missile, likely a Hwasong-12, reached an altitude of about 770 km and travelled 3,700km. This was 1,000km further and 250km higher than the previous ballistic missile test on Aug 29, which too had flown over Hokkaido.

That launch, according to KCNA, was timed to mark the 107th anniversary of the "disgraceful" Japan-Korea treaty of 1910, under which Tokyo colonised the Korean peninsula.

Pyongyang had previously flown missiles over Japan into the Pacific, but the Aug 29 missile test marked the first time it overfly Japan with a missile that is designed to carry a "large-sized" nuclear payload to intermediate-ranges. (In 1998 and 2009, it overflew Japan's main islands with satellite launch vehicles - the Taepodong-1 and Unha-3 vehicles.)

In between its latest two missile test, North Korea conducted its sixth and most powerful nuclear test that packed more power than the atomic bomb that flattened Hiroshima during World War II.

"We need to realise that the consequences are serious. We can't lose sight of the fact that the cycle is moving upward, and for each cycle North Korea becomes that much more potent," Dr Minohara said.

"In that sense there is nothing routine about their missile launches. We are not returning to the point of departure, and with each turn they are becoming more formidable."

Observers have noted that the 3,700km distance flew by Friday's missile puts the US Pacific territory of Guam, which lies 3,400 km away, squarely in the North's crosshairs.

Japan's defence minister Itsunori Onodera said on Friday he believed North Korea "has Guam in mind".

US President Donald Trump has warned of a military response should Pyongyang target Guam after North Korean leader Kim Jong Un threatened on Aug 9 to fire four Hwasong-12 missiles into waters around Guam.

Mr Abe said on Friday a unified international response against North Korea was needed now more than ever. But analysts warn North Korea may well be provoked to act in a more deliberate and forceful manner.

Dr Minohara said that any call for greater sanctions by the global community would need to be weighed against the likely response from Pyongyang, which experts note has built a "sanctions-proof", self-generating economy.

"The sanctions are a slap on the wrist and will not have teeth without Chinese enforcement," Dr Minohara said.

"To add to that, Japan is demanding a complete oil embargo, but there does not seem to be any debate as to the repercussions that may happen because of that."

Short of a total ban on oil supplies, which Beijing has resisted for fear of triggering a collapse in the North, there is practically not much leverage Tokyo has over the Kim Jong Un regime.

Michael Elleman, a missile expert at the International Institute for Strategic Studies, told Washington Post the Aug 29 missile gave North Korea a chance to push the boundaries.

That, it did on Friday.