South Korea’s military said North Korea seemed to have shot a short-range multiple rocket launcher on Sunday, amid rising military tensions on the peninsula following a series of heavier missile tests by the nuclear-armed North.

While they receive far less attention than the enormous intercontinental ballistic missiles (ICBMs), North Korea has recently demonstrated several new types of multiple launch rocket systems, adding to an already extensive arsenal of artillery and rockets capable of striking targets in the South.

“Our military was monitoring the related situation and maintaining a readiness posture this morning in North Korea,” South Korea’s Joint Chiefs of Staff said in a statement, without elaborating.

According to Yonhap news agency, North Korea’s military fired four bullets toward its west coast around 7:20 a.m. (2220 GMT on Saturday) for roughly an hour from an unnamed location in South Pyongan Province.

The National Security Council of South Korea convened an emergency vice-ministerial meeting to discuss the launches.

South Korea approved plans last year to build a $2.6 billion artillery interception system, akin to Israel’s “Iron Dome,” to counter North Korea’s arsenal of long-range weapons and rockets.

About half of South Korea’s 52 million people reside in and around Seoul, which is within range of North Korea’s long-range artillery and numerous rocket launchers.

This year, Pyongyang has launched an exceptionally high number of missiles.

In the midst of stalled denuclearisation talks, South Korea and the US have warned that the North may resume testing of its largest ICBMs for the first time since 2017. North Korea also looks to be preparing to launch a spy satellite, and new building at its shuttered nuclear test site has been discovered.