North Korea fired several cruise missiles early Saturday morning towards the sea west of the Korean Peninsula, according to the South Korean military.

A number of cruise missiles launched since around 4 a.m. Saturday local time (1900 Friday GMT) were detected, South Korea’s Joint Chiefs of Staff said.

It’s Pyongyang’s second missile launch this week since the rare arrival of a U.S. nuclear-armed ballistic missile submarine to South Korea.

It comes as tensions soar on the Korean Peninsula.

On Wednesday, North Korea fired two ballistic missiles, according to Japanese and South Korean militaries, just after the U.S. submarine docked in Busan.

It’s been decades since a U.S. nuclear-armed submarine visited South Korea, and it coincided with allied discussions on a nuclear response in event of a war with the North.

On Thursday, North Korea warned that the deployment of U.S. aircraft carriers, bombers or missile submarines in South Korea could be grounds for a nuclear attack.

Meanwhile, there has been no update on the fate of a U.S. soldier who fled across the military border to the North on Tuesday.

The American facing disciplinary action back home is likely to be in North Korean custody, U.S. officials say, throwing Washington into a new crisis in its dealing with Pyongyang.