North Korean leader Kim Jong Un oversaw a “static firing test of a high-thrust solid-fuel motor” used in long-range nuclear missiles, according to state media on Tuesday, a week after inspecting the motor’s development ahead of his trip to China.

Pyongyang called it the ninth and final test of the engine’s development process, suggesting a test launch of an intercontinental ballistic missile (ICBM) using the engine could take place soon.

The motor uses a newly developed “carbon fiber composite material,” the Rodong Sinmun reported, and the test on Monday “becomes the most strategically significant achievement in the defense technology