The Biden administration is preparing to announce sanctions in response to a massive Russian hacking campaign that breached vital federal agencies, as well as for election interference, a senior administration official said Wednesday night.

The sanctions, foreshadowed for weeks by the administration, would represent the first retaliatory action announced against the Kremlin for last year's hack, familiarly known as the SolarWinds breach. In that intrusion, Russian hackers are believed to have infected widely used software with malicious code that enabled them to access the networks of at least nine agencies, part of what U.S. officials believe was an operation aimed at mining the secrets of the American government.

The measures are to be announced Thursday, according to the official, who was not authorized to discuss the matter by name and spoke on condition of anonymity to The Associated Press.

It was not immediately clear what, if any, other actions might be planned. Officials had previously said they expected to take actions both seen and unseen.

The measures are intended to send a clear retributive message to Russia and to deter similar acts in the future. They come amid an already tense relationship between the U.S. and Russia, with President Joe Biden telling Russian President Vladimir Putin this week that the U.S. would “act firmly in defense of its national interests” regarding Russian intrusions and election interference. But it remained unclear whether the actions would actually result in changed behavior, especially since past measures by the U.S. have failed to bring an end to Russian hacking.

U.S. officials are still grappling with the aftereffects of the SolarWinds intrusion, which affected agencies including the Treasury, Justice, Energy and Homeland Security departments, and are still assessing what information may have been stolen. The breach exposed vulnerabilities in the supply chain as well as weaknesses in the federal government's own cyber defenses.

The actions would represent the second major round of sanctions imposed by the Biden administration against Russia. Last month, the U.S. sanctioned seven mid-level and senior Russian officials, along with more than a dozen government entities, over a nearly fatal nerve-agent attack on opposition leader Alexei Navalny and his subsequent jailing.