SEOUL, South Korea (AP) — North Korea marked the delivery of 250 nuclear-capable missile launchers to frontline military units at a ceremony where leader Kim Jong Un called for a ceaseless expansion of his military’s nuclear program to counter perceived U.S. threats, state media said Monday. Kim said at Sunday’s event in Pyongyang the new launchers would give his frontline units “overwhelming” firepower over South Korea and make the operation of tactical nuclear weapons more practical and efficient. North Korea has been expanding its lineup of mobile short-range weapons designed to overwhelm missile defenses in South Korea, while also pursuing intercontinental ballistic missiles designed to reach the U.S. mainland. North Korea also could seek to dial up tensions in a U.S. election year, experts say. Russia has offered flood aid to North Korea, in another sign of expanding relations between the two nations.