Pyongyang responds to the strikes, launches missiles into the sea

North Korea fired several ballistic missiles into the sea on Monday, hours after South Korean and US troops began large-scale annual joint military exercises, which Pyongyang views as a test of invasion.

South Korean military officials said the missile launch, the fifth such launch by North Korea this year, was detected from North Hwanghae province but did not provide further details such as the distance the projectiles flew.

The statement from the military chiefs said South Korea has strengthened its surveillance posture and is closely cooperating with the United States in this regard.

Early Monday, South Korean and US troops began their annual joint military exercises, which are scheduled to continue for 11 days.

The 'Freedom Shield Command' exercise began after South Korean and US troops suspended live-fire exercises, while Seoul investigated how two of its fighter jets mistakenly bombed civilian areas during a training exercise last week.

The start of the maneuvers was condemned by North Korea, which issued a statement calling the exercises a "dangerous provocative act" that increases the risks of military conflict in the region.

About 30 people were injured, two of them seriously, when two South Korean KF-16 fighter jets mistakenly dropped eight MK-82 bombs on a civilian area in Pocheon, a city near the North Korean border, on Thursday.