North Korea fired several cruise missiles into the Yellow Sea on Wednesday, the South Korean military said.

The missiles were fired at around 7 a.m., South Korea's Joint Chiefs of Staff said.

The missile launches came days after Pyongyang said it conducted a test of an underwater nuclear weapon system in the sea in response to joint military exercises by the United States, South Korea and Japan.

It is believed to be the first time North Korea has test-fired cruise missiles since September last year, when it also conducted launches into the Yellow Sea.

North Korea's state media reported a day after the Sept. 2 launches that the country test-fired two long-range cruise missiles as part of a tactical nuclear strike drill.

On Jan. 14 this year, North Korea test-fired an intermediate-range solid-fuel ballistic missile carrying a hypersonic warhead, the official Korean Central News Agency said the following day.

Tensions on the Korean Peninsula are rising after Pyongyang also fired a barrage of artillery shells near the disputed western maritime boundary with South Korea for three consecutive days early this month, with Seoul conducting a military exercise in retaliation.

Also in January, North Korea tested an underwater nuclear weapon system called the "Haeil-5-23," which is still under development, according a report by KCNA on Jan. 19.

North Korean leader Kim Jong Un, meanwhile, has called for a constitutional change to define South Korea as the North's "primary foe and invariable principal enemy," with the top legislature deciding to abolish entities that promote dialogue with the South, KCNA said last week.

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