It then flew about 621 miles (1,000 kilometers) across the peninsula into the sea in the east.
An official with the South Korean Defense Ministry told CNN that it is assumed a Rodong missile was fired.
"North Korea, by firing of ballistic missile which can equip nuclear warhead, is openly showing its direct and obvious intention of provocation and ambition that it can target our country, including our ports and airports, as well as neighbor countries," the official said.
North Korea is prohibited from carrying out such missile launches under a March U.N. Security Council resolution.
"North Korea, whose provocative acts are threatening the peace and stability of the Korean peninsula and the international community, will be faced with more powerful and thorough sanctions and pressure from the international community and our country."
On July 19, North Korea fired three ballistic missiles off its eastern coast.
Those were believed to be short-range, Scud or Rodong type and flew 300 to 380 miles (500 to 600 kilometers), said Jeon Ha-gyu, spokesman for the South Korean Joint Chiefs of Staff.
North Korean state media said Kim Jong Un, the country`s leader, personally "provided field guidance" for that drill.
Missile tests have become more frequent under Kim Jong Un`s reign. The more tests the reclusive nation carries out, the more it can fix its mistakes, refining and improving its missile technology, experts say.
The South Korean defense official said North Korea has launched more than 30 missiles since Kim took power.
Though the country has continued to improve its nuclear and missile capabilities, it has yet to successfully pair the two.
Last month, South Korea announced it will deploy the advanced U.S THAAD missile defense system in Seongju County, about 155 miles (250 kilometers) southeast of Seoul.
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