North Korea fired what appeared to be cruise missiles off its east coast and air-to-ground missiles from fighter jets on Tuesday on the eve of Pyongyang founder’s birthday, according to the South Korean military.

The surface-to-ship cruise missiles were fired northeastward from areas near its eastern coastal town of Munchon at around 7 a.m. during a time period of more than 40 minutes, the Joint Chiefs of Staff (JCS) said, adding they flew around 150 km, reports Yonhap News Agency.

Along with the missile launches, the North also flew multiple Sukhoi-variant fighter jets above the eastern coastal city of Wonsan, and fired multiple anti-ground missiles into the East Sea, the JCS added.

It was not immediately known if leader Kim Jong-un guided the latest firings.

“The military is closely monitoring the situation for possible additional launches, while maintaining a readiness posture,” Yonhap News Agency quoted the JCS as saying in a statement.

The firings came on the eve of the 108th birthday of Kim Il-sung, the North’s national founder and grandfather of current leader Kim Jong-un.

The founding leader’s birthday is one of the North’s biggest national holidays along with the birthday of the current leader’s father, Kim Jong-il, and the communist nation has often held massive parades and other military events to celebrate the holiday.

It is the latest in a series of military actions by the North.

The last known test of cruise missiles took place on June 8, 2017, when it carried out the first-ever test of its Kumsong-3 coastal defence cruise missile from Wonsan.

The system was first seen at a military parade held in Pyongyang on April 15 of the year to mark the 105th birthday anniversary of the founding leader.

“The projectiles fired today (Tuesday) appear to be similar to those fired in June 2017. More analysis is under way by the South Korean and the US intelligence authorities,” Yonhap News Agency quoted a JCS officer as saying to the media.

Along with smaller-scale artillery firing drills, the communist country has conducted major weapons tests four times so far this year, all in March.

The latest round took place on March 29, when it launched two short-range projectiles from a large-caliber multiple launch guided rocket system into the East Sea.

During the three previous tests, the North showed off its super-large multiple rocket launcher and its version of the ATACMS short-range ballistic missiles, according to the JCS.