North Korea has fired a missile into the Sea of Japan, the first time the isolated state has tested a missile since United States President Donald Trump, took office.
The missile flew about 500 kilometres after being launched from a western region in North Korea.
South Korean officials told Reuters the missile was either of the Rodong medium-range class or another, new type.
It comes as Mr Trump hosts Japanese leader, Shinzo Abe, in Florida this weekend.
The two leaders agreed at earlier talks in Washington the nuclear threat from North Korea was of the highest priority.
Mr Abe said at a joint media conference the firing was "absolutely intolerable".
Mr Trump said at the conference the US "stands behind Japan, its great ally, 100 percent".
The missile was launched from the Panghyon area just before 11am NZ time, the South's Office of the Joint Chiefs of Staff said.
"Our assessment is that it is part of a show of force in response to the new US administration's hardline position against the North," the office said.
Yonhap News Agency said the South Korean military was assessing the launch to confirm whether it was a Musudan intermediate-range ballistic missile, which has a designed flight range of 3000 kilometres (1,800 miles).
North Korea tried to launch a Musudan eight times last year, but most attempts failed. One launch sent a missile 400km more than half the distance to Japan.
North Korean leader Kim Jong Un said in his New Year speech the country was close to test-launching an intercontinental ballistic missile (ICBM) and state media said such a launch could come at any time.
The missile launched on Sunday did not appear to be an ICBM, Yonhap cited a South Korean military source as saying.
Kim's comments prompted a vow of an "overwhelming" response from US Defence Secretary James Mattis when he travelled to South Korea earlier this month.
North Korea has conducted two nuclear tests and several missile-related tests since early last year and was seen by experts and officials to be making progress in its weapons capabilities.
- Reuters / ABC