SEOUL • North Korea's firing of a ballistic missile over Japan yesterday is aimed at showing the United States and its allies it is not lying with its recent threat to strike waters near Guam, experts have said.

They believe the North's focus this time was likely to test the atmospheric re-entry technology of its mid-range ballistic missiles for possible combat use, reported Yonhap news agency.

The missile is believed to be a newly developed intermediate-range ballistic missile, the Hwasong-12. It flew more than 2,700km at a maximum altitude of around 550km.

"Alas, Pyongyang has demonstrated that its threats to the US base on Guam are not a bluff," Mr Konstantin Kosachev, chairman of Russia's Upper House of Parliament's international affairs committee, said on social media. North Korea threatened earlier this month it would fire four Hwasong-12 missiles in the direction of Guam. Yesterday's missile was fired on the standard trajectory of 30 to 45 degrees, a departure from North Korea's usual practice of firing missiles at lofted trajectories, according to Yonhap.

It is still unconfirmed, however, whether the North has mastered the re-entry technology, according to the South's intelligence community. The question is whether the warhead of the missile remained intact at the time of re-entry.

North Korea has tested the Hwasong-12 at least four times, according to the Missile Threat website of the US Centre for Strategic and International Studies.

The first successful Hwasong-12 test occurred on May 14 from a location near Kusong city.

That missile flew for 700km and reached an altitude of more than 2,000km before landing in the Sea of Japan or East Sea. At that time, it was fired at a lofted angle to avoid flying over Japan.

North Korea has conducted over 80 missile tests since Mr Kim Jong Un came to power in late 2011 following the death of his father Kim Jong Il, but none of them flew over Japan.

The two intercontinental ballistic missiles fired last month were launched at lofted trajectories.

North Korea watcher Ankit Panda wrote on The Diplomat website that Pyongyang needs to test missiles on a more realistic trajectory to give its missile scientists "important diagnostic information to eventually improve its airframe designs" and to further advance its nuclear and missile programme.

Yesterday's missile was fired from a site in Sunan district near Pyongyang.

US officials noted that if it was launched from the capital's outskirts, it might have been designed to complicate recent US threats to hit the North with pre-emptive strikes as any strike near Pyongyang would risk many civilian deaths, reported The New York Times.