No further details were given, including the type of missiles or the firing location, a break from past practices that suggests the US military may still be trying to determine such details amid fears that the communist nation could have tested an ICBM.

Earlier, South Korea's Joint Chiefs of Staff said that the North fired four ballistic missiles from an area near the North's Dongchang-ri long-range missile site that Pyongyang has used to fire long-range rockets.

That raised fears the North could have tested an ICBM, but the JCS said such a possibility is low.

The missiles flew about 1,000 kilometers before splashing into the East Sea, the JCS said.

The latest firings are seen as a show of force in response to the ongoing annual joint military exercises between South Korea and the United States that the North has long denounced as a rehearsal for an invasion of the country.

The launches also came three weeks after the North test-fired a new intermediate-range ballistic missile powered by solid fuel.

Weapons experts say solid-fuel missiles pose greater threats as they require less launch preparation time than liquid-fueled rockets, and can be fired from mobile launchers, which are easy to move around.

The latest provocations could have an impact on the North Korea policy that the administration of US President Donald Trump is putting together. News reports said that the Trump administration is considering a wide range of options, including preemptive strikes.

North Korean leader Kim Jong-un said in his New Year's Day address that the North entered the final stage of preparations to test-fire an ICBM, an apparent threat that he is close to perfecting capabilities to strike the continental US with a nuclear missile.

In response, Trump said the North's development of such a missile "won't happen." (Yonhap)