North Korea said Tuesday it would strengthen its atomic arsenal in an angry response to upcoming joint US-South Korean military exercises which the communist state denounced as nuclear war games. The North justified its possession of nuclear weapons as establishing a balance of power to prevent a nuclear holocaust, ahead of the joint war games in South Korea starting Saturday. "The exercises will be nuclear war exercises aimed to invade the North to all intents and purposes in view of their nature, scope and contents," a foreign ministry spokesman told the official Korean Central News Agency. "The DPRK (North Korea) will take necessary counter-measures including the bolstering of its nuclear arsenal to cope with the extremely hostile attempt of the US to bring down the system in the DPRK though it is the Korean people's own choice," he said.