WASHINGTON — Russia has fired scores of guided missiles into Ukraine, but on Saturday it claimed for the first time that it had launched one capable of hypersonic speed in an attack on an ammunition depot in western Ukraine. The report could not be independently verified, but if true could be the first use of a hypersonic weapon in combat. Hypersonics, generally defined as weapons capable of flying at speeds over Mach 5, or five times the speed of sound, are at the center of an arms race among the United States, Russia and China. The United States has pursued development of this type of weapon since the early 2000s, focusing on two different variants, according to a report released Thursday by the Congressional Research Service. The first is a “hypersonic glide vehicle” which is launched from a rocket and then separates before gliding to a target, and the second is a faster version of a cruise missile, which could be launched by submarines, ships, airplanes and ground vehicles, the report said. The Pentagon requested $3.8 billion for hypersonic research in fiscal year 2022.