(LEAD) N. Korea fires multiple ballistic missiles toward East Sea: JCS

North Korea fired multiple ballistic missiles toward the East Sea on Monday, South Korea's military said, less than two weeks after it launched a suspected hypersonic ballistic missile.

The Joint Chiefs of Staff (JCS) said it detected the launch at about 9:20 a.m. from the Pyongyang area and the missile flew more than 900 kilometers.

"The South Korean military has stepped up its surveillance to prepare for additional launches and is maintaining an all-out readiness posture, while closely sharing relevant information with the United States and Japan," the JCS said in a notice.

The latest launch came after the North fired one ballistic missile from the Wonsan area toward the East Sea on Oct. 3.

North Korean state media reported the following day that Pyongyang launched an intermediate-range strategic missile as part of efforts to train missile troops operating the "hypersonic strategic weapon system."

Monday's launch also came just days after South Korea conducted its first test launch of a hypersonic glide vehicle (HGV) on Thursday in an apparent show of force against North Korea following last month's land mine blast south of the border.

Tensions between the two Koreas have heightened since the Sept. 21 explosion on the South's side of the Demilitarized Zone (DMZ) that injured three South Korean soldiers, two of them critically.

The JCS concluded its recent joint investigation with the U.N. Command that found land mines deliberately planted by North Korean troops were behind the cause of the blast.

Pyongyang has flatly denied responsibility for the incident, accusing Seoul of fabricating the findings, and warning of "immediate and merciless" retaliation if Seoul takes counteraction.