WASHINGTON—The U.S. government accused the Chinese of being the world's "most active and persistent" perpetrators of economic spying, an unusual move designed to spur stronger U.S. and international action to combat rampant industrial espionage threatening U.S. economic growth.

Russian intelligence agents also are conducting extensive spying to collect U.S. economic data and technology, according to a U.S. intelligence report released Thursday that concluded China and Russia are "the most aggressive...