A North Korean drone crashed on a South Korean Island near their disputed border.
Soon after, the countries’ artillery batteries exchanged fire across the western sea border.
Meanwhile, U.S. officials are expressing concern over the tensions on the Korean peninsula.
A state department spokesperson said the North is quote: “needlessly threatening regional peace and security.”
Monday, North Korea fired 500 artillery shells as part of a military exercise.
South Korea fired back, after officials there said some shells fell into South Korean waters.