The United States and South Korea hold a joint military exercises . Hide Caption 8 of 10 Photos: Pyongyang says that constitutes a grave provocation . The North `` will further bolster up its nuclear deterrent for self-defence as long as the U.S. , the world 's biggest nuclear weapons state , persists in its hostile policy , '' KCNA cited the Foreign Ministry spokesman as saying . South Korea says the flag was to mark territory and was not used as a target .
The United States and South Korea hold a joint military exercises . Hide Caption 8 of 10 Photos: Pyongyang says that constitutes a grave provocation . South Korea says the flag was to mark territory and was not used as a target .