North Korea fired a submarine-launched ballistic missile on Saturday, but the launch appears to have failed in the early stages of flight, South Korea's military said.

The launch comes a day after the U.S. and South Korea pledged to deploy an anti-missile system to counter threats from Pyongyang, and two days after North Korea warned it was planning its toughest response to what it deemed a "declaration of war" by the United States. That followed Washington's blacklisting of the nation's leader, Kim Jong Un, for alleged human rights abuses.