North Korea's nuclear weapons should be ready for use at "any moment," leader Kim Jong Un said, according to state media on Friday.
The order came after the United Nations imposed its strongest sanctions yet on Pyongyang, in response to a nuclear test carried out by North Korea in January.
While attending a rocket test on Thursday, Kim said the military should also be ready to carry out pre-emptive attacks, North Korea's official KCNA news agency reported.
Kim stressed "the need to get the nuclear warheads deployed for national defence always on standby so as to be fired any moment," he was reported as saying.
Communist North Korea's nuclear and military activity this year has heightened tensions on the peninsula and brought international condemnation.
It carried out a nuclear test on January 6, a long-range rocket launch on February 7 and fired a series of projectiles into the sea off its eastern coast on Thursday.