"We have intelligence that North Korea fired short-range missiles into the waters off its western coast, and we are trying to confirm how many were fired and what type of missiles they are," a Defense Ministry official said on customary condition of anonymity.
South Korea's Yonhap news agency reported the North fired one or two missiles Thursday morning, citing an unnamed intelligence official.
Last month, North Korea test-fired at least one short-range missile into eastern coastal waters, which South Korean and U.S. officials played down as part of the communist country's regular military drills.
The latest launches come as North Korea refuses to move on its pledge to shut down its main nuclear reactor over a delay in withdrawing US$25 million (EUR18.4 million) at a Macau bank, which was blacklisted by the U.S.
The North has made the funds' release a key condition to disarmament, having boycotted international negotiations for more than a year over the issue, during which it conducted a nuclear test last October.
Last July, North Korea also fired a barrage of missiles, including a long-range one believed to be capable of reaching even parts of the U.S.