South Korean President Park Geun-hye says her country must make it clear the North Korean regime will not survive if it does not give up its nuclear program.
Park made the remarks in a televised speech for newly commissioned military officers Friday, a day after North Korean leader Kim Jong Un ordered his military to be ready to use its nuclear weapons "at any moment."
Park said to expect a fiercer backlash than usual from North Korea in response to new international sanctions on Pyongyang that went into effect Wednesday.
Also Friday, a North Korean cargo vessel was stopped in the Philippines after inspections mandated by the new sanctions resulted in the discovery of some safety violations.
The MV Jin Teng was held in Subic Bay, Philippines, north of Manila. A report to the coast guard said inspectors found no suspicious cargo, but spotted safety violations such as missing or damaged equipment that must be corrected before the ship can leave port.
On Thursday, North Korea fired six short-range missiles off its eastern coast, according to Seoul's Defense Ministry, which said the projectiles flew up to 150 kilometers before landing in the sea.
The North Korean news agency also quoted Kim on Friday threatening to carry out "a preemptive attack" on his country's enemies.
North Korea often threatens nuclear strikes during times of elevated tensions. But experts question whether the North has the ability to place its nuclear weapons on long-range missiles.