North Korea has fired a ballistic missile from a submarine on Saturday, but it appears to have failed soon after launch, South Korea's military said.
The launch comes at the end of a week of sharply rising tensions on the Korean peninsula.
It comes only a day after the US and South Korea pledged to deploy an advanced anti-missile system to counter threats from Pyongyang.
The development also comes two days after North Korea warned it was planning its toughest response to what it deemed a "declaration of war" by the United States.
The warning was in response to Washington's blacklisting of the isolated state's leader Kim Jong Un for alleged human rights abuses.
The blacklisting drew a sharp and swift protest from neighbuoring China, Pyongyang's sole major ally. Beijing said on Friday it lodged complaints with the US and South Korean ambassadors over the THAAD decision.
The South's Office of the Joint Chiefs of Staff said in a statement that the missile was launched at about 11:30am Seoul time (0230 GMT) in waters east of the Korean peninsula.
The missile was likely fired from a submarine as planned but appears to have failed in the early stage of flight, the Joint Chiefs said.
South Korea's Yonhap news agency said the missile's engine successfully ignited but the projectile soon exploded in mid-air at a height of about 10 km.
It added that the missile had covered not more than a few kilometers across the water.
South Korea's military declined to confirm those details.
The missile was detected in the sea southeast of the North Korean city of Sinpo, South Korea's military said.
The US Strategic Command also said on Saturday it had tracked what it believed was a KN-11 submarine-launched ballistic missile fired from North Korea's east coast port of Sinpo.
The command said in a statement the missile was tracked over the Sea of Japan, "where initial indications are it fell" into the sea between the North and Japan.
The North American Aerospace Defense Command (NORAD) determined the missile did not pose a threat to North America, the statement added.
Satellite images indicate Pyongyang is actively trying to develop its submarine-launched ballistic missile program in this area, according to experts.
US, Japan and S Korea condemn launch
Neighbouring Japan, the United States, and South Korea's military condemned the missile launch as a flagrant violation of UN sanctions.
The missile launch is a "clear challenge to UN Security Council resolutions," Japanese Prime Minister Shinzo Abe said on Saturday, according to Kyodo news agency.
"We should strongly condemn the launch by working with the international community," Abe told reporters.
Abe said the launch did not gravely affect Japan's national security.
The US State Department condemned North Korea's firing of a submarine-launched ballistic missile on Saturday.
It said the missile test violated UN Security Council resolutions, which explicitly prohibit North Korea's use of ballistic missile technology.
"We call on North Korea to refrain from actions that further raise tensions in the region and focus instead on taking concrete steps toward fulfilling its international commitments," the State Department said in a statement.
The statement said the US was monitoring and assessing the situation in close coordination with its regional allies and partners.
"These actions, and North Korea's continued pursuit of ballistic missile and nuclear weapons capabilities, pose a significant threat to the United States, our allies, and to the stability of the greater Asia-Pacific," said Gabrielle Price, for the Bureau of East Asian and Pacific Affairs at the US Department of State.
The UN Security Council imposed harsh new sanctions on the country in March for its nuclear test and rocket launch.
North Korea rejects the sanctions as infringement of its sovereignty and its right to space exploration. Pyongyang also conducted a test of a submarine-launched ballistic missile (SLBM) in April, calling it a "great success" that provided "one more means for powerful nuclear attack".
A report on 38 North, a website run by the US-Korea Institute at Johns Hopkins University in the US, said in May that North Korea’s submarine-launched ballistic missile program is making progress,
But it appeared that the first ballistic missile submarine and operational missiles are unlikely to become operational before 2020, the report added.
China holds combat drill in the South China Sea
The Chinese navy conducted combat drills near its southern island province of Hainan and the Paracel islands in the South China Sea, the Ministry of Defense said on Saturday.
The drills come ahead of a July 12 ruling by the Hague-based Permanent Court of Arbitration on a case brought by the Philippines disputing several of China's territory claims in the South China Sea.
Ships from China's northern, eastern and southern fleets participated in Friday's drills, which focused on air control, surface operations and anti-submarine warfare, among other training exercises, the ministry said in a website statement.
China claims nearly all the South China Sea, but its claims overlap in part with those of Brunei, Malaysia, the Philippines, Taiwan and Vietnam.
China has repeatedly said it does not consider any decision reached by the arbitration court to be legally binding.
"China adheres to the position of settling disputes through negotiation and consultation with states directly concerned," state news agency Xinhua said in a commentary on Saturday.
The US State Department spokesperson John Kirby said in a statement issued on Friday that, "as provided in the Law of the Sea Convention, the tribunal’s decision in this case will be legally binding on both parties, the Philippines and China."
"It’s our expectation that both parties will comply with their obligations and exercise restraint," he added.