Shortly before Seoul was set to release its new submarine, South Korea officials claim that the North has fired a missile believed to be a short-range one into the waters off the Korean Peninsula’s east coast.

In a statement, the South Korean Joint Chiefs of Staff said that the projectile was launched on Tuesday, at around 6:40 in the morning. It said that the South’s troops are “maintaining a readiness posture” for probable “additional launches.”

The North’s test was said to be “regrettable for happening at a time when political stability on the Korean peninsula is very critical,” according to Boo Seung-chan, South Korea’s Defense Ministry’s spokesman, who spoke in a briefing on Tuesday.

The recent test has already been the subject of consultations between the US military’s Indo-Pacific Command in Hawaii and partners and allies.

“While we have assessed that this event does not pose an immediate threat to US personnel or territory, or to our allies, the missile launch highlights the destabilizing impact of (North Korea’s) illicit weapons program,” stated the US military.

International law does not allow Pyongyang to test nuclear weapons and projectiles. The United Nations Security Council has slammed the North with sanctions over its test in the past.

The test firing came on the heels of the presence of Kim Song, North Korea’s representative, to the UN General Assembly. During the event, he brought up the division between the two Koreas and slammed the US for its alleged interference in the peninsula.

“Inter-Korean relations have never come out of the shadow of US interference and obstruction,” he said as he noted Washington-Seoul’s close ties.

The recent testing marks the North’s third this September. Long-range cruise missiles were also released by Pyongyang last Sept. 11 and 12, CNN reported.

The two Koreas then tested ballistic missiles on Sept. 16, which further intensified the already tension-ridden region.