A few hours after South Korea and the US started joint military exercises, North Korea fired some ballistic missiles into the sea. North Korea views the military exercise between the two countries as a rehearsal for an attack.

This is North Korea's fifth missile launch this year. Missiles were fired from North Korea's Hwanghai province on Monday, South Korea's military said. But it is not clear how far those missiles flew, according to South Korean officials. South Korea's Joint Chiefs of Staff said it has strengthened its surveillance position and is coordinating closely with the US.

South Korea and the US military started the exercise on Monday and is scheduled to last until June 11. Nuclear-armed North Korea has condemned the two countries' joint military exercises. North Korea says the exercise is a "dangerous provocation" and "will increase the risk of military conflict".

Last week, two South Korean fighter jets mistakenly bombed a residential area. South Korean authorities are investigating that. After the incident, the armies of the two countries suspended the live-fire training and started the 'Freedom Shield Command Post' exercise.