The White House said in a statement on Thursday that Russia's foreign intelligence service, known as the SVR, was responsible for the SolarWinds hack, which led to the compromise nine federal agencies and hundreds of private sector companies.
Senior US government officials had already said the Russian government was responsible for the sprawling cyber attack, but Thursday's announcement offers the first formal statement pinning the operation on a specific agency.
The White House statement was paired with a series of sanctions against five Russian cybersecurity firms, which the Treasury Department said had been involved in supporting Russian cyber operations.