China on Monday accused Washington of breaking into computers at a university that U.S. officials say does military research, adding to complaints by both governments of rampant online spying against 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 a commercial security provider, Qihoo 360 Technology Co., traced the attacks to the National Security Agency but didn’t say how that was done.

China and the United States are, along with Russia, regarded as global leaders in cyberwarfare research.

China accuses the United States of spying on universities, energy and internet companies and other targets. Washington accuses Beijing of stealing commercial secrets and has announced criminal charges against Chinese military officers.