North Korea fired what appeared to be two cruise missiles into the sea off its east coast on Tuesday, days after a flurry of ballistic missile tests.
South Korea's Joint Chiefs of Staff said it is assessing the launches to determine the nature of the projectiles.
Such a launch would be its fifth missile test of the year, as North Korean leader Kim Jong Un has vowed to bolster the military with cutting-edge technology at a time when talks with South Korea and the United States have stalled.
The isolated nation's biggest flurry of missile launches since at least 2019 has prompted an expression of concern from the UN secretary general, and the Biden administration has applied new sanctions.
Cruise missile launches by the North are not banned under United Nations sanctions imposed on Pyongyang, which has defied international condemnation and conducted four rounds of ballistic missile tests, the most recent on January 17.
China and Russia have pushed the UN Security Council to remove a ban on Pyongyang's exports of statues, seafood and textiles, and raise a refined petroleum imports cap.
North Korea has said it is open to talks, but only if the United States and others drop "hostile policies" such as sanctions and military drills.
It has defended its missile tests as its legitimate right to self-defence and said the US was intentionally escalating tensions by imposing new sanctions, state media said.
The US has called on the United Nations Security Council to take action against several North Korean individuals and entities accused of violating security council resolutions that ban North Korea's missile and nuclear weapons development.
US Secretary of State Antony Blinken said the country had made clear it had no hostile intent towards North Korea and was willing to engage in talks without preconditions, but that the tests were "profoundly destabilising."
The North Korean foreign ministry said that while Washington may talk of diplomacy and dialogue, its actions show "it is still engrossed in its policy for isolating and stifling" the country.
"The US is intentionally escalating the situation even with the activation of independent sanctions, not content with referring the DPRK's just activity to the UN Security Council," the statement said.
