"The ICBM-class ballistic missile launched this time, if calculated based on the trajectory, depending on weight of warhead, could have a flying range of over 15,000 kilometres (9,320 miles). In which case the whole of the US territory would be within the range," said Shingo Miyake, parliamentary vice-minister of defence.

Miyake said the projectile appeared to have flown about 1,000 kilometres (620 miles) with a maximum altitude of more than 6,000 kilometres (3,720 miles) before landing outside Japan's exclusive economic zone.

He later said authorities would still need to definitively confirm it was an ICBM.

"Based on the flying distance and the maximum altitude of the ballistic missile launched this time, we think it is an ICBM-class ballistic missile, but we are analysing further details," he said.

But Prime Minister Fumio Kishida unequivocally condemned the launch, as well as the test-firing of a shorter-range missile on Sunday night.

The launches are "not only a clear violation of UN Security Council resolutions but also a threat to peace and stability of the region and we strongly condemn (them)", Kishida said.