North Korea launched a submarine-launched ballistic missile (SLBM) at around 5:30 am Wednesday, South Korea’s Joint Chiefs of Staff (JCS) said, revealing the launch to have occurred near Sinpo, a port in North Korea’s northeast.

The missile – likely a Pukkuksong-1 SLBM (known as the KN-11 in South Korea and the United States) – traveled some 500km, JCS later confirmed, adding the launch “showed progress compared to several firing tests in the past”.

The test comes just two days after South Korea and the U.S. kicked off joint Ulchi Freedom military drills on Monday, which will last until September 2.