SEOUL: North Korea fired a short-range ballistic missile into the sea off its east coast on Friday, South Korea's military said, the latest in a series of launches by the nuclear-armed country amid heightened tensions.

South Korea called it a violation of a 2018 bilateral military agreement banning "hostile acts" in the border area.

South Korea also scrambled fighter jets when a group of about 10 North Korean military aircraft flew close to their heavily fortified border, and North Korea fired some 170 rounds of artillery into "sea buffer zones" off its east and west coasts, the South's Joint Chiefs of Staff (JCS) said.

South Korea's National Security Council (NSC) condemned the North for escalating tensions.

Seoul imposed its first unilateral sanctions against Pyongyang in nearly five years, blacklisting 15 North Korean individuals and 16 institutions involved in missile development.

The JCS issued a warning to North Korea, urging it to stop provocations and escalating tension.

Yoon's spokesman said the South Korean government respects inter-Korean agreements and the cancellation of the 2018 military accord depends on Pyongyang's behaviour.

The incidents came after KCNA said leader Kim Jong Un oversaw the launch of two long-range strategic cruise missiles on Wednesday to confirm the reliability of nuclear-capable weapons deployed to military units.

South Korea's JCS said the latest missile was launched at 1:49 a.m. on Friday (1449 Thursday GMT) from the Sunan area near North Korea's capital, Pyongyang, and flew about 700 km (435 miles) to an altitude of 50 km at a speed of Mach 6.

Japan's coast guard also reported the launch, which was at least the 41st ballistic missile test by the North this year.

Although there were no signs of panic among South Koreans, a Gallup poll released on Friday showed more than 70% of respondents said North Korea's missile tests threatened peace, the highest since the North's sixth nuclear test in 2017.