North Korea has fired a suspected ballistic missile, hours after the United States separately deployed B-1B bombers for allied air drills.

Japan's defence ministry and also South Korea’s Joint Chiefs of Staff said the launch occurred on Wednesday but gave no further details, such as how far the missile flew.

The launch comes as South Korea and the United States prepare to wrap up 11 days of combined military drills, which Pyongyang has denounced.

The B-1B bombers conducted separate air drills with warplanes from South Korea and Japan earlier on Wednesday.

Earlier this week, North Korea’s state media said leader Kim Jong-un called for the military to be constantly ready for combat to thwart plans by its rivals to invade.

North Korea's ballistic missiles are banned by United Nations Security Council resolutions that have imposed strict sanctions on the nuclear-armed country.