A South Korean defence ministry official said today there was no evidence yet that North Korea had fired a missile.
The statement countered claims by Japanese and US officials confirming the launch of an anti-ship missile.
The South Korean official declined to comment on an earlier confirmation by a source at Seoul's intelligence agency that Pyongyang had fired an anti-ship missile into the Yellow Sea between the Korean Peninsula and China this morning.
Japanese officials said in Tokyo the missile was believed to be of a type having a range of just 37.5 miles; US defence officials in Washington confirmed the launch of what one called "an anti-ship missile".
North Korea has fired at least two other short-range missiles this year into the Sea of Japan, and there have been reports that it was preparing to fire a ballistic missile capable of reaching Japan.
Those previous launches in the past two months, involving similar missiles, were apparently part of regular military exercises.