North Korea has fired a suspected ballistic missile off its east coast, its first known test since June, South Korean military officials have said.
It came after a US aircraft carrier arrived in South Korea to participate in joint drills, and ahead of a planned visit by Vice President Kamala Harris.
Seoul said the launch was an "act of grave provocation".
The UN prohibits North Korea from ballistic and nuclear weapons tests.
South Korea's military said it detected a short range missile fired at just before 07:00 local time (11:00 GMT) close to Taechon, more than 100 km (60 miles) north of Pyongyang. It said it flew about 600 km at an altitude of 60 km.
"Our military maintains a full readiness posture and is closely cooperating with the US while strengthening surveillance and vigilance," it said in a statement.
Japan's coast guard confirmed the launch, warning ships to "be vigilant". Tokyo's defence minister Yasukazu Hamada said the missile reached a maximum altitude of around 50 km, falling in waters off North Korea's eastern coast, and outside Japan's exclusive economic zone.
"It's North Korea's way of showing defiance of the [US] alliance," Soo Kim, an analyst at the Rand Corporation, told AFP.
The nuclear-powered USS Ronald Reagan docked in the southern port city of Busan on Friday, to take part in joint drills off South Korea's east coast. The exercises are for the "sake of peace and stability on the Korean peninsula", according to the South Korean navy.
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Ms Harris will visit South Korea in the coming days as part of a trip to the region that will include the funeral of former Japanese Prime Minister Shinzo Abe.
Tensions on the Korean peninsula have spiked in the past year, with Pyongyang firing a number of ballistic missiles.
South Korea's President, Yoon Suk-yeol, who took office in May, has promised a tougher stance on North Korea and indicated closer ties with the US.
Earlier this month, North Korea passed a law declaring itself to be a nuclear weapons state, with leader Kim Jong-un ruling out the possibility of talks on denuclearisation. Despite widespread sanctions, Pyongyang conducted six nuclear tests between 2006 and 2017.