Reports suggest North Korea's biggest missile test ever may not have been what it seemed, raising new questions over the secretive country's banned weapons program.

North Korea said it had test-fired its new Hwasong-17 intercontinental ballistic missile (ICBM) on Thursday, the first test of a missile that size since 2017.

North Korean state media heralded the launch as an "unprecedented miracle," and South Korean and Japanese officials independently confirmed flight data that showed it flew higher and longer than any previous test.