Jong-un vows to make N Korea world's strongest nuclear power
North Korean leader Kim Jong-un has pledged to make his country "the world's strongest nuclear power" as he hailed the scientists behind the country's recent intercontinental ballistic missile (ICBM) launch, according to the state media. North Korea has test-fired 23 missiles this year, including a hydrogen bomb that was about 4-5 times stronger than the 1945 Nagasaki nuclear bomb.