North Korean leader Kim Jong Un guided the first test of a large new solid-fuel rocket engine at the country’s main spaceport on Thursday, according to state media, in a sign of progress on plans to build long-range nuclear missiles that can be launched more quickly in a conflict.

The Academy of Defense Science “successfully made the static firing test of a high-thrust solid-propellant motor with a thrust of 140tf (tons of force)” under Kim’s guidance, the Rodong Sinmun reported Friday, calling it “the first of its kind in the DPRK.”