Reports of North Korea artillery drill as U.S. submarine docks in South

The USS Michigan, a nuclear-powered submarine has made aport call in South Korea (Photo: Reuters)

North Korea conducted a big live-fire exercise on Tuesday to mark the foundation of its military, media reported, as a U.S. submarine docked in South Korea in a show of force amid growing concern over Pyongyang's nuclear and missile programs.

The port call by the USS Michigan came as a U.S. aircraft carrier strike group steamed toward Korean waters and as the top envoys for North Korea policy from South Korea, Japan, and the United States met in Tokyo.