North Korea fired four short range ballistic missiles into the West Sea on Saturday, continuing military provocations for the fourth consecutive day.

According to Seoul’s Joint Chiefs of Staff, South Korean military detected four short range ballistic missiles fired from North Pyongan Province from 11:32 a.m. to 11:59 a.m.

The missiles flew about 130 kilometers, reaching altitude of 20 kilometers, the JCS said, adding that South Korean and US militaries are currently carrying out further analysis.

North Korea began a series of provocations on Wednesday, firing 25 projectiles of various specification, and continued missile launches on Thursday. One of the missiles fired on Wednesday landed near South Korean waters south of the de facto maritime border NLL in the East Sea. One of the missiles fired on Thursday is thought to be an intercontinental ballistic missile. The ICBM, however, failed in midflight.

On Friday, the North did not fire missiles but carried out a large scale air drill, prompting South Korea to scramble fighter jets in response.

The JCS, meanwhile, said that the Seoul-Washington joint air drill Vigilant Storm was concluded on Saturday. The drill involved two US Air Force B-1B bombers, making the first time since December 2017 the bomber has entered South Korean airspace.