The launch came days after US aircraft carriers USS Carl Vinson and USS Ronald Reagan left those waters after joint exercises with the South Korean navy.
The North has carried out two atomic tests and dozens of missile launches since the beginning of past year in its quest to develop a missile capable of delivering a nuclear warhead to the continental United States - something President Trump has vowed "won't happen".
South Korean President Moon-Jae-in has been briefed on the latest launch, the military said, declining to give further details.
The four are the North's military unit handling ballistic missiles Strategic Rocket Force, Koryo Bank, Kang Bong General Trading Corp. and Korea Kumsan Trading Co.
The missile was believed to be a Scud-class ballistic missile and flew about 450 km (280 miles), South Korean officials said.
"Through such a provocation, North Korea will only gain worldwide isolation and economic difficulties, while losing the opportunity to develop", the president was quoted as saying at the session, according to Cheong Wa Dae spokesperson Park Soo-hyun.
Bolivia's U.N. Ambassador Sacha Llorentty Soliz, the current U.N. Security Council president, told reporters Thursday he had not received any requests for a meeting on the latest launches.
North Korea has rejected all UN Security Council resolutions dating back to 2006 when it conducted its first nuclear test, saying such moves directly infringe its sovereign right to self-defense.
Moon has sought to expand cross-border civilian exchanges as a way to improve ties, but North Korea on Monday rejected a Seoul civic group's offer to provide anti-malaria supplies to protest South Korea's support of fresh United Nations sanctions adopted last week.
In what will likely become another source of animosities, Moon's government said Thursday that it will let two of the four North Korean fishermen recently rescued at sea resettle in the South in accordance with their wishes.
Pyongyang often accuses Seoul of kidnapping its citizens or enticing them to defect to the South.
The launches Thursday were North Korea's fourth missile test in as many weeks as the country continues to speed up its development of nuclear weapons and missiles. Roh Jae-cheon, the South Korean military spokesman, said the objective of the North Korean tests was likely to " show off its ability to precisely target a large warship". The improved range indicates the North is pursuing weapons capable of reaching US aircraft carriers that operate from deeper positions, he said.
Moon, who has said he wants to try to resolve the North's nuclear crisis through dialogue, also has suggested that South Korea must "learn to say no" to Washington.
The new tests come a day after South Korea suspended deployment of a controversial United States missile defence system - an apparent concession to China, which is strongly opposed to the Terminal High Altitude Area Defense (THAAD) system.