Senate Intelligence Committee chairman Mark Warner, D-Va., is cautioning that a major cyberattack against Ukraine could have possible ripple effects on nearby NATO members – and force NATO allies to come to their defense.

Warner made the comments Thursday afternoon in an interview on NPR's All Things Considered.

"If you shut down Polish hospitals because they can't get power to take care of their people, you're rapidly approaching what could be viewed as an Article 5 violation of NATO, which basically says if you attack one NATO nation – and Poland is a NATO nation – all of the remaining 29 nations need to come to their assistance," he said. "We are in an uncharted territory."

Warner said he believed the Ukrainian people would continue to fight back against the Russian invasion and form an "insurgency," which would be harder for Russian President Vladimir Putin's forces to counter.

"It's again one thing to knock out a government. It's another thing to fight an insurgency led by the Ukrainian people across all of this captured territory," he said.

Warner said the U.S. would have to support the insurgency but do it in a way that would avoid a direct conflict with Russia.

"We've managed to keep the peace for 80 years. Vladimir Putin has violated that. He has to pay a price. But we don't want to default this to [a] NATO-Russia conflict," he said.

Still, Warner said that publicizing U.S. intelligence about Russia's plans in Ukraine – such as the fact that Putin intended to use a false flag operation to justify an invasion of Ukraine – helped unite allies against the Kremlin.

"We now have not only America and NATO, we have countries like Japan, South Korea, Singapore, Australia all weighing in with sanctions, as well," Warner said. "Matter of fact, the only person that I've heard that's come to Putin's defense in the last 72 hours has been the former president of the United States, which is pretty stunning in my mind."

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