North Korea fired multiple short-range projectiles into the East Sea on Monday morning, South Korea’s Joint Chiefs of Staff said. Three of them flew approximately 200 kilometers and reached a peak altitude of 50 kilometers, from Sondok in South Hamgyong Province along the North’s eastern coast.

“The launches were part of the North’s annual joint strike drills on Feb. 28 and March 2,” the South’s JCS said, noting the three projectiles could be super-large rockets with a caliber of 600 millimeters, similar to ones Pyongyang launched a week ago during its first weapons test on March 2.

Of the three projectiles, the first two were fired 20 seconds apart, as were the two projectiles in the first weapons test. It took more than a minute to fire the last two. The first weapons test involved rockets with a smaller caliber of 300 or 240 millimeters, the JCS added.

The military and experts agree that the North is trying to improve the performance of its multiple-launch rocket systems. But experts leaned toward the idea that Pyongyang has already put the advanced rockets into combat operation.

“With those rockets in place, the North could just be checking on them to see better performance,” said Kim Dong-yub, an analyst from Seoul’s Institute for Far Eastern Studies.

North Korean watchers speculate that the latest launches were also a protest against European countries that had condemned the North for its initial firings a week earlier, when they described the test as “provocative actions” that violated UN resolutions aimed at pressing Pyongyang to abandon its nuclear weapons.

Cheong Wa Dae reiterated its earlier response that the launches were not conducive to peace on the Korean Peninsula. Pyongyang called the office “mentally challenged” when Seoul expressed concerns over the prior firings the previous week.

By Choi Si-young (siyoungchoi@heraldcorp.com)