Kim preparing for nuke tests? US warns N. Korea of response as tensions escalate

• The South Korean and U.S. militaries flew 20 fighter jets over waters off South Korea's western coast Tuesday in a continued show of force as a senior U.S. official warned of a forceful response if North Korea goes ahead with its first nuclear test explosion in nearly five years. South Korea's Joint Chiefs of Staff said the air demonstration involved 16 South Korean planes — including F-35A stealth fighters — and four U.S. F-16 fighter jets and was aimed at demonstrating their ability to swiftly respond to North Korean provocations. Watch this video for more.