North Korea fired a submarine-launched ballistic missile off its east coast on Saturday, but the missile failed in its initial flight stage, South Korea's Joint Chiefs of Staff (JCS) said, according to the Seoul-based Yonhap News Agency.
An official at Seoul's Defense Ministry on Saturday couldn't immediately confirm how far the projectile traveled and where it landed.
"North Korea have achieved a measurable success in mastering technology for mid-range ballistic missiles, that can reach Guam, with nuclear payload through its sixth attempt and likewise, they will continue to test launch SLBM until they get it", Dr. Koh Yuwhan, a professor at North Korean studies at Dongguk University in Seoul, said.
Reclusive North Korea and the rich, democratic South are technically still at war because their 1950-53 conflict ended in an armistice, not a peace treaty.
"The North launched what was believed to be an SLBM from waters off the port of Sinpo at around 11:30 a.m. (0230 UTC)", the South Korean Defense Ministry said in a statement.
North Korea's acquiring the ability to launch missiles from submarines would be an alarming development for rivals and neighbours because missiles from submerged vessels are harder to detect in advance.
North Korea, believed to be developing nuclear weapons, is banned by the United Nations from any use of ballistic missiles.
The launch comes a day after the USA and South Korea pledged to deploy an anti-missile system to counter threats from Pyongyang, and two days after North Korea warned it was planning its toughest response to what it deemed a "declaration of war" by the United States. This followed a North Korean space launch in February that was condemned by the U.N. Security Council as a test of a long-range missile in disguise and the country's fourth nuclear test a month earlier.
The latest launch came a day after USA and South Korean military officials said they were ready to deploy an advanced US missile defense system in South Korea to cope with North Korean threats.
North Korea previously fired an SLBM on April 23 in a test hailed as an "eye-opening success" by leader Kim Jong-Un, who at the time declared his country had the ability to strike Seoul and the U.S. whenever it pleased. China, Russia and North Korea all say the THAAD deployment could help US radars spot missiles in their countries.
The North's foreign ministry called the sanctions against Kim "the worst hostility and an open declaration of war", vowing to take "the toughest countermeasures to resolutely shatter the hostility of the U.S.".
North Korea has already been sanctioned heavily because of its nuclear weapons program. "We have to cooperate with the global community and condemn North Korea", he told public broadcaster NHK. However, the action by the Obama administration on Wednesday marked the first time Kim has been personally targeted, and also the first time that any North Korean official has been blacklisted by the U.S. Treasury in connection with reports of rights abuses.