North Korea’s leader, Kim Jong Un, watched a ground test of a solid-fuel missile engine and saw new tanks put through their paces recently, the country’s official news agency reported Sunday. The engine, made with carbon fiber materials, is part of a plan to steadily upgrade the country’s strategic strike capability, according to the Korean Central News Agency. The report provided no information on where and when the inspections took place. “The South Korean and U.S. intelligence authorities are closely monitoring North Korean military’s weapon development trends,” South Korea’s Ministry of National Defense said by text message Monday. The engine test is of great significance in putting the country’s military muscle on the highest level, Kim said in the KCNA report.