North Korea fired multiple cruise missiles off its east coast on Sunday, South Korea's Joint Chiefs of Staff said.
It did not specify how many missiles were launched, but said it has strengthened monitoring and vigilance and was working with the United States to analyze the latest launch.
North Korea is stepping up confrontation with the United States and its allies, but officials in Washington and Seoul say they have spotted no signs Pyongyang intends to take imminent military action.
Kim Jong Un's government is likely to continue or even increase provocative steps, officials and analysts say, after it made strides in ballistic missile development, bolstered cooperation with Russia and scrapped its decades-long goal of peacefully reuniting with South Korea.