North Korea fires missile, flies warplanes

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

South Korea also scrambled fighter jets on Friday when a group of about 10 North Korean military aircraft flew close to the border dividing the two countries, and North Korea fired some 170 artillery shots off its east and west coasts, the South's Joint Chiefs of Staff (JCS) said.

South Korea's National Security Council condemned the North for escalating tension, calling its moves a violation of a 2018 bilateral military pact that bans "hostile acts" in the border area.

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

North Korea's official KCNA news agency quoted the country's military as saying it took "strong military countermeasures" after South Korean artillery-fire drills on Thursday.

The incidents followed a KCNA report on Thursday that leader Kim Jong-un had overseen the launch of two long-range strategic cruise missiles on Wednesday to confirm the reliability of nuclear-capable weapons deployed to military units.

The unprecedented frequency of North Korea's missile launches has raised concerns it may be preparing to resume testing of nuclear bombs for the first time since 2017. Some analysts do not expect any tests before neighbouring China concludes a congress of its ruling Communist Party, which begins on Oct. 16.

The US Indo-Pacific Command said it was aware of the latest missile launch and had assessed that "it does not pose an immediate threat to US personnel or territory, or to our allies."

"We will continue consulting closely with our allies and partners to monitor the DPRK's destabilising ballistic missile launches," it said, referring to North Korea by the initials of its official name.

South Korea's Joint Chiefs of Staff said the missile was launched on Friday from the Sunan area near North Korea's capital Pyongyang. It was at least the 41st ballistic missile launch by North Korea this year.

Japan's coast guard also reported the launch.

The South Korean JCS statement said the aircraft incident happened late on Thursday and early Friday Korean time.

North Korea has called its most recent series of missile tests, which included an intermediate range ballistic missile that flew over Japan last week, a show of force against joint South Korean and US military drills.