SEOUL, South Korea — North Korea threatened Tuesday to take “bold and decisive military steps” against Japan as it slammed Tokyo’s adoption of a national security strategy as an attempt to turn the country into an aggressive military power. The North’s statement came four days after Japan announced a security strategy that reflects its determination to possess “counterstrike” capability and double its military spending to gain a more offensive footing against threats from China and North Korea. The statement said North Korea wants to make sure it can take “bold and decisive military steps” to protect its sovereignty and national interests in the wake of the complexity of regional security caused by the Japanese security strategy.