A North Korean test of an apparent hypersonic missile appeared to have ended in a midair explosion over the Sea of Japan early Wednesday, South Korea’s military said.

A South Korean military source said that the weapon appeared to have been a solid-fueled hypersonic missile that flew about 250 kilometers before exploding, scattering debris over a radius of several kilometers and falling into the sea, the Yonhap news agency reported.

South Korea is working with the U.S. and Japan to analyze the launch, Seoul said, adding that more smoke than usual had been seen in pictures of the apparent failure, indicating that the cause could be related to combustion issues with a solid-fueled engine.