BEIJING: A Chinese police agency on Monday accused the United States of breaking into computers at a university that American officials say does military research, adding to complaints by both governments of rampant online spying on each other.

Northwestern Polytechnical University reported computer break-ins in June, the National Computer Virus Emergency Response Center announced. It said the center, working with commercial security provider Qihoo 360 Technology Co., traced the attacks to the National Security Agency (NSA), but gave no details of how that was done.