North Korean leader Kim Jong Un has overseen test flights of hypersonic missiles, state news agency KCNA reported on Monday.
The drill was carried out on Sunday under Kim's supervision, the agency said.
The hypersonic missiles were launched from Pyongyang towards the north-east and hit their intended targets 1,000 kilometres away, it said.
KCNA said Kim defended the drill as "a very important strategic task to maintain and expand a powerful and reliable nuclear deterrent."
The information provided by North Korean authorities could not be independently verified.
On Monday, Japanese news agency Kyodo, citing the Japan Coast Guard, said two suspected ballistic missiles had been fired.
South Korean news agency Yonhap, citing Seoul's military, reported that the missiles flew towards the East Sea, also known as the Sea of Japan.
Yonhap quoted the general staff in Seoul (JCS) as saying that it had detected the launches.
North Korea is prohibited by UN resolutions from launching or even testing ballistic missiles of any range. These are usually surface-to-surface missiles that can also be equipped with a nuclear warhead.
Pyongyang has significantly expanded its missile tests over the past two years, while sharpening its rhetoric against the US and South Korea. It has also strengthened its military cooperation with Russia.
