The U.S. military and intelligence agencies are still analyzing test launch data to determine what kind of missile was fired and how far it went.
It is not yet known whether the missiles were short, medium or long range, such as an intercontinental ballistic missile (ICBM).
The US monitors all North Korean weapons tests via radar and satellites. US satellites can detect the heat signatures of a missile launch almost instantly.
Earlier in the day, the South Korean Joint Chiefs told reporters that North Korea had launched an unidentified missile in the direction of the sea between the Korean peninsula and Japan.
The Japanese Coast Guard has warned ships to be on the lookout for falling debris.