The U.S. military’s Indo-Pacific Command called it a “ballistic missile launch.”

North Korea fired an “unknown projectile” on Wednesday which appeared to fail immediately after launch, South Korea’s military said, amid reports that the nuclear-armed North is seeking to test-fire its largest missile yet.

The United States and South Korea have warned that North Korea may be preparing to launch an intercontinental ballistic missile at full range for the first time since 2017.

The projectile was fired from Sunan Airport outside the North Korean capital of Pyongyang, South Korea’s Joint Chiefs of Staff said in a statement.

It is presumed that it failed immediately after launch, the author of the statement said. The projectile seemed to explode in mid-air shortly after liftoff, Yonhap news agency reported, citing unnamed sources.

A source at Japan’s Ministry of Defence also called the projectile a potential ballistic missile, Japanese public broadcaster NHK reported.

Debris fell in or near Pyongyang after the failed test, Seoul-based NK News reported, citing unnamed witnesses and a photograph of the test showing a red-tinted ball of smoke at the end of a zig-zagging rocket launch trail in the sky above the city.