Secretary of State Mike Pompeo says Russia was pretty clearly behind the grave cyberattack against the United States, the first administration official to publicly tie the Kremlin to the widespread intrusion at a time when President Donald Trump has kept silent on the failure to protect government and private-sector computer networks.

Its not clear exactly what the hackers were seeking, but experts say it could include nuclear secrets, blueprints for advanced weaponry, COVID-19 vaccine-related research, and information for dossiers on key government and industry leaders.

Were still unpacking precisely what it is, and Im sure some of it will remain classified, Pompeo said in an interview late Friday with radio talk show host Mark Levin. But suffice it to say there was a significant effort to use a piece of third-party software to essentially embed code inside of U.S. government systems and it now appears systems of private companies and companies and governments across the world as well. This was a very significant effort, and I think its the case that now we can say pretty clearly that it was the Russians that engaged in this activity.

Russia has said it had nothing to do with the hacking.