North Korean leader Kim Jong-un watches the test-fire of two short-range ballistic missiles on Thursday, in this undated picture released by North Korea's Central News Agency on July 26. Reuters

North Korea launched two more projectiles believed to be short-range ballistic missiles into the East Sea, Saturday, according to the South Korean military, the latest in a series of saber-rattling moves protesting a joint exercise between Seoul and Washington.

The projectiles were fired at 5:32 a.m. and 5:50 a.m. from the vicinity of the eastern coastal city of Hamhung, South Hamgyong Province, and flew around 400 kilometers at a maximum altitude of 48 km and a top speed of around Mach 6.1, the Joint Chiefs of Staff (JCS) said.

"We see high chances of additional launches, as North Korea is now carrying out summertime drills and the combined exercise between South Korea and the U.S. is underway," the JCS said in a press release.

"Accordingly, we have been closely monitoring the situation, while maintaining the appropriate military readiness," it added.

This is the fifth series of launches since July 25 when Pyongyang fired the first set of two short-range missiles. It came just four days after the North launched two projectiles believed to be the newly developed short-range KN-23 ballistic missiles, also into the East Sea.