Kim Jong-un has ordered North Korean scientists to construct a missile that will be the largest in the regime's arsenal and to have it ready to be launched on September 9, the 70th anniversary of the founding of the republic, according to a defector.

His account suggests the North Korean leader issued the order at a two-day meeting of senior military leaders and scientists in Pyongyang in mid-December.

The defector has not been named, but was described by Japan's Mainichi newspaper, as someone who was involved in the regime's missile programme and has retained links to contacts in the North.

He told the newspaper the missile will be designated the Unha-4 and will be a larger version of the Unha-3, a three-stage vehicle which North Korea claims is a rocket designed to put satellites into orbit.

An Unha-3 was successfully launched from the Sohae Satellite Launching Station, in the far north-west of the country, in February 2016.