State-sponsored Russian hackers are actively seeking to hijack essential internet hardware, US and UK intelligence agencies say.

Britain’s National Cyber Security Centre (NCSC), the FBI, and the US Department of Homeland Security issued a joint alert on April 16, warning that the global campaign could be escalated to launch future offensive attacks.

The NCSC has published on its website a Joint US – UK statement on malicious cyber activity carried out by Russian government said, “the targets of the malicious cyber activity are primarily government and private-sector organisations, critical infrastructure providers, and the internet service providers that support these sectors.”

In a press conference about the alert, White House cyber-security coordinator Rob Joyce said the US and its allies had “high confidence” that Russia was behind the “broad campaign”.

Intelligence gathered by the US and UK suggested that millions of machines directing data around the net were being targeted, he said. The hackers also sought to undermine the firewalls and intrusion-detection system devices.

“Russian state-sponsored actors are using compromised routers to conduct spoofing ‘man-in-the-middle’ attacks to support espionage, extract intellectual property, maintain persistent access to victim networks and potentially lay a foundation for future offensive operations,” the NCSC said. “They could be prepositioning for use in times of tension,” said the NCSC’s head, Ciaran Martin,

Britain and the United States said they issued the alert to help targets protect themselves and persuade victims to share information with government investigators.

Moscow has refused to comment on the allegations after it previously denied all accusations that it carried out cyber attacks on other countries.