Short-range ballistic missiles are being fired in this file photo from the North Korea's Korean Central Television on July 26, 2023. Yonhap

North Korea fired around 10 short-range ballistic missiles into the East Sea on Thursday, the South Korean military said, a day after sending hundreds of large balloons carrying trash and manure into the South.

The Joint Chiefs of Staff (JCS) said it detected the flight vehicles presumed to be short-range ballistic missiles fired from the Sunan area in Pyongyang at 6:14 a.m. toward the East Sea. It did not provide further details as an analysis is currently under way.

Though the North has used missile launches as a message to the outside world, it is unusual for it to fire a barrage of some 10 missiles at one time.

The South Korean military condemned the launches, which put the Seoul metropolitan area and key air bases within range, as a "provocative act" that threatens the Korean Peninsula and vowed a stern response to the North's provocations.

"Our military has strengthened monitoring and vigilance against additional launches, while closely sharing information related to North Korean ballistic missiles with the U.S. and Japanese authorities," the JCS said in a text message to reporters.

The missile launches came after the North sent hundreds of large balloons carrying trash and fecal matter to the South on Tuesday and Wednesday after warning of a "tit-for-tat action" against anti-Pyongyang leaflets sent by activists in South Korea.

The firings also came after the North failed in an attempt to launch a second military spy satellite Monday as the space rocket carrying the satellite exploded during the first-stage flight shortly after liftoff.

The latest launches mark Pyongyang's first ballistic missile launch since May 17, when it test-fired tactical ballistic missiles equipped with what it called a new "autonomous" navigation system, considered to be short-range ballistic missiles. (Yonhap)