"North Korea fired an unspecified ballistic missile toward the East Sea on Monday," Seoul's Joint Chief of Staff said, according to the official Yonhap news agency, referring to the body of water also known as the Sea of Japan.

The office of Japan's prime minister also tweeted Monday morning that "North Korea has launched a suspected ballistic missile."

The Japanese Coastguard said soon after that the projectile "appears to have already fallen," without providing further details.

The United States and South Korea on Sunday staged joint air drills featuring a strategic bomber and stealth fighter jets in response to a North Korean intercontinental ballistic missile (ICBM) launch a day earlier.

Japan said the ICBM had flown for 66 minutes and landed in its exclusive economic zone (EEZ).

North Korea later said the missile launched Saturday was a Hwasong-15 and was part of a "surprise" drill to demonstrate Pyongyang's capacity to carry out a "fatal nuclear counterattack".