South Korean officials say North Korea test-fired what appears to be a submarine-launched ballistic missile off its eastern coast.

An official at Seoul's Defense Ministry on Saturday couldn't immediately confirm how far the projectile traveled and where it landed.

North Korean efforts to develop submarine-launched missile systems are a serious concern for rivals and neighbors because missiles from submerged vessels are harder to detect in advance.

The launch came a day after U.S. and South Korean military officials they're ready to deploy an advanced U.S. missile defense system in South Korea to cope with North Korean threats.