North Korea fired an unidentified projectile off its east coast on Thursday, South Korea said, hours after Pyongyang dismissed US President Donald Trump's decision to scale back military exercises with South Korea.

South Korea's Joint Chiefs of Staff announced the launch but did not immediately provide further details about the projectile.

The Japanese prime minister's office said it detected the suspected launch but gave no further details either.

It came after North Korea said a US decision to scale back military exercises with South Korea did not change what it sees as the provocative nature of the drills, dampening hopes for an early resumption of diplomacy between North Korean leader Kim Jong Un and Trump.

The sister of North Korean leader Kim Jong Un made the comments late on Wednesday night in her country’s first reaction to Trump’s moves to drastically cut back the annual US-South Korean military drills.