US Secretary of State Mike Pompeo said on Friday that Russia was "clearly" behind a massive cyberattack executed earlier this week that breached several US government agencies.
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Microsoft said late Thursday that it had notified more than 40 customers hit by the malware, which security experts say could allow attackers unfettered network access to key government systems and electric power grids and other utilities.
"There was a significant effort to use a piece of third-party software to essentially embed code inside of US government systems," Pompeo told The Mark Levin Show on Friday.
"This was a very significant effort, and I think it's the case that now we can say pretty clearly that it was the Russians that engaged in this activity."
Roughly 80% of the affected customers are located in the United States, Microsoft president Brad Smith said in a blog post, with victims also found in Belgium, Britain, Canada, Israel, Mexico, Spain and the United Arab Emirates.
The threat comes from a long-running attack which is believed to have injected malware into computer networks using enterprise management network software made by the Texas-based IT company SolarWinds, with the hallmarks of a nation-state attack.
The National Security Agency called for increased vigilance to prevent unauthorized access to key military and civilian systems.
Security analysts have said the attacks pose threats to national security by infiltrating key government systems, while also creating risks for controls of key infrastructure systems such as electric power grids and other utilities.
The US Cybersecurity and Infrastructure Security Agency said government agencies, critical infrastructure entities, and private sector organizations had been targeted by what it called an "advanced persistent threat actor."
CISA did not identify who was behind the malware attack, but private security companies pointed a finger at hackers linked to the Russian government.
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Pompeo had also suggested Moscow's involvement on Monday, saying the Russian government had made repeated attempts to breach US government networks.
US President-elect Joe Biden expressed "great concern" over the computer breach while Republican Senator Mitt Romney blamed Russia and slammed what he called "inexcusable silence" from the White House.
i24NEWS contributed to this report.
