North Korea has fired another missile into the sea, according to neighbouring countries.
In an emergency National Security Council meeting, the South Korean government expressed regret over what it called "a short-range missile launch" by the North on Tuesday.
South Korea's military earlier said the object, fired from North Korea's mountainous northern Jagang province, flew toward the waters off the North's eastern coast.
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The US Indo-Pacific Command said in a statement the launch did not pose an immediate threat to US personnel, territory or allies.
However, it said the missile launch did highlight "the destabilising impact of (North Korea's) illicit weapons programme", adding the US commitment to the defence of South Korea and Japan "remains ironclad".
Details of the launch were being analysed by South Korean and US authorities, and Japanese Prime Minister Yoshihide Suga said North Korea fired "what could be a ballistic missile", adding his government had stepped up its vigilance and surveillance.
Watch: North Korea monitored by Carrier Strike Group.
A ballistic missile launch would violate a UN Security Council ban on North Korean ballistic activities, but the council typically does not impose new sanctions on North Korea for launches of short-range weapons.
As the North's latest missile launch was detected by its rivals, North Korean Ambassador Kim Song used his speech on the last day of the UN General Assembly to justify his country's development of a "war deterrent" to defend against US threats.
"The possible outbreak of a new war on the Korean Peninsula is contained not because of the US's mercy on the DPRK (Democratic People's Republic of Korea), it is because our state is growing a reliable deterrent that can control the hostile forces in an attempted military invasion," Mr Kim said.
It comes after tests of ballistic and cruise missiles earlier this month, North Korea's first such launches in six months.
The tests displayed North Korea's ability to attack targets in South Korea and Japan, both key US allies, where a total of 80,000 American troops are stationed.
And the latest weapon tests by Pyongyang raise questions about the sincerity of its offer for talks with Seoul.
Last week, Kim Yo Jong, the influential sister of North Korean leader Kim Jong Un, reached out to Seoul, saying her country was open to resuming talks and reconciliatory steps if conditions were met.
South Korea has called Ms Kim's statement "meaningful" but urged North Korea to restore communication channels before any talks between the rivals can be arranged.
A UK Foreign, Commonwealth & Development Office spokesperson said: "The UK condemns North Korea's decision to launch a short-range ballistic missile, in violation of UN Security Council Resolutions.
"The UK remains committed to the goal of denuclearisation of the Korean Peninsula and commends the diplomatic efforts of the US and regional partners to seek peace on the Korean Peninsula and preserve regional stability. We urge North Korea to return to dialogue."