A U.S. surveillance aircraft has been seen flying over South Korea a second time in just a few days.

The aviation tracker Aircraft Spots reported on Wednesday that it spotted the U.S. Navy’s EP-3E aircraft in skies over South Korea on Tuesday on an apparent mission to monitor North Korea.

This was two days after the North fired what is believed to be two short-range ballistic missiles from the eastern coastal city of Wonsan toward the East Sea. 

It marked the fourth major weapons test the North has conducted this year.

The United States flew the same type of plane over the peninsula on Sunday, the same day the North fired the two projectiles.