North Korea fired an artillery shot, presumably from a multiple rocket launcher, for a second straight day on Monday amid the U.S. deployment of six F-35A stealth fighters on the Korean Peninsula for the allies' combined military exercise.

According to the South Korean military on Wednesday, it detected a single trajectory believed to be an artillery shot on Monday morning, a day after the regime fired two such rounds into the Yellow Sea.

While an official at the National Security Office said the launches are believed to be a part of the North's regular training, it has also been suggested that they could be in protest of the allies' training drills involving the F-35A stealth fighters.

It is the first time that the U.S. has publicly deployed the aircraft since December 2017.

The military said Seoul and Washington are working in close coordination to maintain a thorough readiness posture.