A South Korean military official declined to confirm the report but said the military was analysing the launch.
North Korea fired an unidentified projectile on Sunday, South Korea's military said, a week after it test-fired a mid-long range missile which experts said marked an advancement in the reclusive state's missile programme.
South Korea's Office of Joint Chiefs of Staff said in a statement that the projectile took off Sunday afternoon from a location near Pukchang, an area where Pyongyang attempted to test-launch another missile last month but failed and added that South Korea and the United States were conducting close-up analysis of the launch.
The missile flew about 500 kilometers (310 miles) and was believed to have landed in waters off its east coast, South Korea's military said.
The office did not give further details, but Yonhap News Agency said it was not believed to be an intercontinental ballistic missile (ICBM), citing an anonymous source.
A South Korean military official declined to confirm the report but said the military was analysing the launch.
North Korea has defied all calls to rein in its nuclear and missile programmes, even from China, its lone major ally, calling them legitimate self-defence.
It has been working to develop a nuclear-tipped missile capable of striking the U.S. mainland.
"Today the U.S. mainland and the Pacific operational theatre are within the strike range of the DPRK and the DPRK has all kinds of powerful means for annihilating retaliatory strike," North Korea's state KCNA news agency said in a commentary on Saturday.
The White House released a statement saying it is aware of the latest North Korea missile launch and noted that this system has a "Shorter range than the missiles launched in North Korea's three most recent tests."
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 "china, kcna, pyongyang, north korea, missile, south korea, intercontinental ballistic missile (ICBM), Pukchang, Pyongyang")
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