The US Cybersecurity and Infrastructure Security Agency said it registered a cyberincident "impacting enterprise networks across federal, state, and local governments, as well as critical infrastructure entities and other private sector organizations."
According to the CNN, on Tuesday, O'Brien held a phone conversation with counterparts from the UK, Canada, Australia and New Zealand and proposed to issue a joint statement condemning the cyberattack, which some officials blame on Russia.
The proposed joint statement is now being considered, however it is unclear if any condemnation would name Russia, the broadcaster said, citing one of the Five Eyes sources.
US intelligence and security agencies have already formed a Cyber Unified Coordination Group (UCG) to coordinate a whole-of-government response to this cyberattack.
Last week, reports emerged that hundreds of US federal government entities and companies had been targeted by a massive cyberattack, which was instantly blamed on a foreign actor by US media. The hackers reportedly got access by compromising the Texas-based SolarWinds software. The company provides remote information technology services around the world, including several US government agencies and the military.
The Washington Post claimed a hacking group with links to Moscow was behind it but provided no evidence to back the allegation. Kremlin spokesman Dmitry Peskov has refuted these claims.
On Saturday, President Donald Trump suggested China rather than Russia may be behind the cyberattacks. Trump also said the true scale of the cyberattacks had been exaggerated by the media and the situation was under control.