South Korea has confirmed that North Korea sustained serious damage from the South Korean military’s counterattack following the North’s artillery attack on the South’s Yeonpyeong Island on Tuesday.

Shin Hyeon-don of the Joint Chiefs of Staff said Friday that surveillance satellite images showed traces of damage by South Korean self-propelled guns at North Korean military bases on Mu Island and in Gaemeori.

Shin added that a bunker for coastal artillery collapsed at the Mu Island base.

He said that more time is needed to accurately assess the extent of the damage to the North.