The U.S. Air Force has carried out joint air drills with South Korea that included a flyover by a pair of supersonic, nuclear-capable B-1B bombers. The weekend military exercises came as the U.S. and South Korea agreed to extend war games involving hundreds of warplanes and thousands of troops. The drills came as North Korea test-fired more than 30 missiles over the past week, including an intercontinental ballistic missile on Thursday that triggered evacuation alerts in Japan.