Kim Jong Un watches North-Korean war-like practice drills after the start of annual combined military drills by the Us and South Korea.
North Korea has said since last week that it had tested "strategic" cruise missiles, implying they may be designed to carry nuclear warheads.
In recent months, the North has tested an array of weapons that include ballistic missile systems that are under development and an underwater drone.
"If the enemy opt for military confrontation ... our army should deal a deadly blow to annihilate them thoroughly," KCNA news agency quoted Kim as saying.
“North Korean leader Kim Jong Un instructed various agencies to find ways to comprehensively support Palestine in the war between Israel and Hamas,” Korea Broadcasting System reported.
The reclusive North has one of the most highly controlled societies in the world, with leader Kim Jong Un accused of using a system of patronage and repression to retain absolute power.
On Tuesday North Korean state media said leader Kim Jong Un had reviewed spy satellite photos of the White House, Pentagon and US aircraft carriers at the naval base of Norfolk.
North Korea must "push ahead with the work for exponentially boosting the production of nuclear weapons and diversifying the nuclear strike means," said Kim Jong Un.
Kim inspected a Russian fighter jet factory that is under Western sanctions, nuclear-capable strategic bombers, hypersonic missiles and warships last week.