YEONPYEONG ISLAND, South Korea — A South Korean official say sounds of artillery have been heard on the country's Yellow Sea island attacked earlier this week by North Korea.

It was not immediately clear where the artillery sounds were coming from.

An official at the South Korean Joint Chiefs of Staff says the sounds of artillery were heard twice on the island and that military officials are trying determine the details. The official spoke on condition of anonymity.

The sounds come as the North warns that U.S.-South Korean military drills planned for this weekend are pushing the peninsula to the brink of war.

It also comes after a U.S. military commander toured the wreckage from a North Korean artillery attack this week.