North Korea fired at least one short-range ballistic missile overnight that landed in the sea off its east coast, the latest in a series of missile tests defying world pressure and threats of more sanctions.
The missile was believed to be a Scud-class ballistic missile and flew about 450km, South Korean officials said.
North Korea has a large stockpile of the short-range missiles, originally developed by the Soviet Union.
This launch followed two successful tests of medium- to long-range missiles in as many weeks.
North Korea has been conducting such tests at an unprecedented pace in an effort to develop an intercontinental ballistic missile capable of hitting the mainland United States.
It was likely showing its determination to push ahead with missile development in the face of international pressure to rein it in and "to pressure the [South Korean] government to change its policy on the North", South Korea's Joint Chiefs of Staff spokesman Roh Jae-cheon said.
It was the third ballistic missile test-launch since South Korea's liberal President Moon Jae-in took office on 10 May pledging to engage the reclusive state in dialogue.
Mr Moon says sanctions alone have failed to resolve the growing threat from the North's advancing nuclear and missile programme.
The missile reached an altitude of 120km, Mr Roh said. "So far, the assessment is there was at least one missile but we are analysing the number of missiles," he said.
North Korea, which has conducted dozens of missile tests and tested two nuclear bombs since the start of 2016 in defiance of UN Security Council resolutions, says the programme is necessary to counter US aggression.
The White House said President Donald Trump had been briefed on the launch.
The US Pacific Command said it tracked what appeared to be a short-range ballistic missile for six minutes and assessed it did not pose a threat to North America.
The United States has said it was looking at discussing with China a new UN Security Council resolution and that China, North Korea’s main diplomatic ally and neighbour, realises time was limited to rein in the North's weapons programme through negotiations.
US Defense Secretary Jim Mattis, asked what a military conflict with North Korea might look like if diplomacy failed, warned yesterday that would be "probably the worst kind of fighting in most people's lifetimes".
"The North Korean regime has hundreds of artillery cannons and rocket launchers within range of one of the most densely populated cities on Earth, which is the capital of South Korea," Mr Mattis told CBS news programme Face the Nation.
"And in the event of war, they would bring danger to China and to Russia as well," he said.
Japan lodged a protest against the North's latest missile launch, which appeared to have landed in Japan's exclusive economic zone.
Japanese Prime Minister Shinzo Abe vowed action along with other nations to deter North Korea's repeated provocations.
"As we agreed at the recent G7, the issue of North Korea is a top priority for the international community," Mr Abe told reporters in brief televised remarks. "Working with the United States, we will take specific action to deter North Korea."
South Korea's new liberal administration has said North Korea's repeated test launches were dashing hopes for peace on the Korean peninsula.
Mr Moon swiftly called a meeting of the National Security Council, South Korea's Office of the Joint Chiefs of Staff said in a statement.
North Korea last test-fired a ballistic missile on 21 May off its east coast and said last night it had tested a new anti-aircraft weapon supervised by leader Kim Jong-un.
It has tested Scud-type short-range missiles many times in the past, most recently in April, according to US officials.
However, experts say it may be trying to test new capabilities that may be fed into its efforts to build an ICBM.
"There are many possibilities ... It could have been a test for a different type of engine. Or to verify the credibility of the main engine for ICBM's first stage rocket," said Kim Dong-yub, a military expert at Kyungnam University's Far Eastern Studies department in Seoul.
Modified versions of the Scud have a range of up to 1,000km.
Tomorrow, the United States will test an existing missile defence system to try to intercept an ICBM, the first such test, officials said last week.