The South Korean military has retracted its initial assessment that North Korea fired an apparent intermediate-range ballistic missile on Monday.

It later disclosed the missile flew some 1,100 kilometers before landing in the sea, falling short of the flight range usually covered by a midrange missile.

Now, it says Pyongyang has fired a suspected hypersonic missile capable of flying more than five times the speed of sound, using solid fuel.

Yonhap News Agency reported on the possibility the North adjusted the volume of fuel to shorten the flight distance, and that the South Korean military may have not accurately detected the supersonic missile flying at a low altitude.

The launch came as US Secretary of State Antony Blinken was holding talks with South Korean Foreign Minister Cho Tae-yul in Seoul.

South Korean media outlets reported that the latest launch may be an attempt to test how the US may react, two weeks ahead of President-elect Donald Trump's inauguration.

South Korean military sources meanwhile revealed that activities involving a mobile launch pad equipped with a missile continue to be monitored in North Korea, prompting the military to step up vigilance against further missile launches.