US President Joe Biden delivered a stern warning on June 16 to his Russian counterpart Vladimir Putin over ransomware attacks emanating from Russia, saying he was prepared to retaliate against any cyber assaults on US infrastructure.

Speaking after the two leaders’ first summit in Geneva, Biden said he laid down the line on Moscow not taking action against hackers who have extorted hundreds of millions of dollars from western governments, companies and organisations, purportedly from the safety of Russian soil.

In a separate press conference following the three-and-a-half hours of discussions, Putin rejected the allegations and insisted that the US itself was behind a large number of cyberattacks.

But he acknowledged that the issue was “extremely important” and said the two sides agreed to hold formal consultations on it. “We need to drop all insinuations, sit down at an expert level and start working in the interests of the US and Russia,” Putin said.

Experts claim that Russia and neighbouring countries have become the hub of what is called “ransomware-as-a-service”, in which different groups work together to hack and then export a target, promising to free up blocked computers after being paid off.

US victims include hospitals, school systems, police departments and myriad businesses.

Washington officials say they don’t believe the Russian government is directly involved, but say it harbours hackers that should be arrested.

Assistant Attorney General John Demers told a conference held by the Cyberscoop media group on June 16: “There is a lot of ransomware activity that is coming from [within] Russian borders, which isn’t being conducted by Russian government officials, but is being tolerated by the Russian government.

“They’re not just tolerating this – they are actively getting in the way of US law enforcement efforts to combat this type of hacking,” he alleged.

The subject was ripe for discussion at the Geneva summit after apparently Russia-based hackers hijacked the computers of a major US oil distribution network, Colonial Pipeline, on May 7 and demanded millions in ransom.

Weeks later, a different group of seemingly Russian hackers did the same with JBS, one of the world’s biggest meat processors, which paid $11 million in bitcoin to regain control of its information technology systems.

Both hacks had significant economic impact in the US – Colonial was forced to shut down fuel pipelines, forcing gas prices to soar, and beef prices rose as JBS had to curtail production.

Biden has fielded political criticism domestically for not taking any visible action in retaliation, though the US military’s Cyber Command declines to make public any actions it takes against adversaries.

The US leader said he delivered to Putin a list of 16 areas of crucial infrastructure like energy and water that are “off limits” to attack, drawing a red line for Moscow.