North Korea early on Sunday fired an unidentified projectile into the sea off the east coast of the Korean peninsula, the South Korean military said, according to Reuters.
The object was launched from an area in North Korea's western region, the South's Office of the Joint Chiefs of Staff said in a statement.
No further details were provided.
The statement follows an earlier report in the South Korean Yonhap news agency which said that the North had fired a ballistic missile.
North Korea carried out two nuclear tests last year, and has been under sanctions since 2006.
The UN voted to impose new sanctions on the country last November, following its repeated nuclear tests.
North Korean leader Kim Jong Un said in January that the country was close to test-launching an intercontinental ballistic missile (ICBM). State media later said that such a launch could come “at any time”.
U.S. President Donald Trump responded to Kim’s recent threats by tweeting, “North Korea just stated that it is in the final stages of developing a nuclear weapon capable of reaching parts of the U.S. It won't happen!”
A statement posted by the White House just after Trump took office said the Trump administration intends to develop a "state of the art" missile defense system to protect against attacks from Iran and North Korea.