North Korea launched a ballistic missile from a submarine off its east coast Saturday morning, a South Korean Defense Military official said.

The missile was fired about 11:30 a.m. local time from waters off the city of Sinpo, said the official, who asked not to be identified in line with government policy. It was launched successfully but appears to have failed in early flight, the official said, without providing details.

The launch came a day after South Korea and the U.S. agreed to deploy the so-called Thaad anti-ballistic missile system in the Korean peninsula. That followed North Korea’s description of recent financial sanctions against leader Kim Jong Un as a “declaration of war.” The North has conducted a series of ballistic missile tests since April.