North Korea has fired a ballistic missile from a submarine off its east coast, say the US and South Korea.

The KN-11 missile was launched from waters near Sinpo and flew about 500km (300 miles) before falling into the Sea of Japan, a US official said.

Japan's PM said it fell inside Japan's Air Defence Identification Zone, calling it a "reckless act".

It comes as South Korea and the US begin annual military drills, which routinely anger Pyongyang.

Ulchi Freedom involves about 80,000 US and South Korean troops in a largely computer-simulated defence of South Korea from a fictional North Korean invasion.