The launch came hours after US President Trump announced plans to meet Kim Jong Un later this year.
North Korea fired around 10 short-range ballistic missiles toward the sea on Thursday, South Korea's military said.
Seoul's Joint Chiefs of Staff said the North fired the missiles "from its Pyongyang area."
Earlier, the Japanese prime minister's office and the country's Coast Guard also said they detected the suspected launch.
The incident came hours after US President Donald Trump said he would meet North Korean leader Kim Jong Un later this year.
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