(Bloomberg) -- The U.S. is working to determine who carried out a cyberattack on Ukrainian government websites and it wouldn’t be surprising if Russia was behind it, President Joe Biden’s national security adviser Jake Sullivan said.

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Ukrainian officials say “all evidence” points to Russia, while Russia denies it was behind the hacks. It’s the latest source of tension after President Vladimir Putin massed 100,000 troops on the Ukrainian border for what the U.S. says is a possible invasion.

“We’re working hard on attribution,” Sullivan said on CBS’s “Face the Nation” on Sunday. “This is part of the Russian playbook, so it would not surprise me one bit if it ended being attributed to Russia.”

“And yes of course, if it turns out that Russia is pummeling Ukraine with cyberattacks and if that continues over the period ahead, we will work with our allies on the appropriate response,” he said.

Kremlin spokesman Dmitry Peskov told CNN that last week’s inconclusive diplomacy by the U.S. and Europe to head off a possible Russian military move against Ukraine was a “disturbing” outcome.

“There are some understandings between us,” Peskov said in an interview with “Fareed Zakaria GPS” aired Sunday. “But in general, in principle, we can now say that we are staying on different tracks, on totally different tracks, and this is not good, and this is disturbing.” 

The Biden administration said Friday that Russian actors are preparing potential sabotage operations against their own forces and fabricating provocations in social media to justify an invasion into Ukraine if diplomacy fails. 

Russia says it wants NATO to bar Ukraine and other ex-Soviet states from membership and to roll back its forces to positions they held in 1997.

Sullivan reiterated that the U.S. and its allies have warned Russia it will face “severe economic consequences and a price to pay” if its troops move into Ukraine.

GOP Critics

Republican lawmakers called for more forceful action now, such as a permanent halt to the Nord Stream 2 natural-gas pipeline from Russia to Germany. 

The U.S. should let Putin know “that Nord Stream 2 pipeline is not going to operate,” Senator Mitt Romney said on NBC’s “Meet the Press.”

“Rather than threatening after an invasion takes place, we ought to be providing deterrence before an invasion takes place,” Representative Michael McCaul of Texas, the top Republican on the House Foreign Affairs Committee, said on CNN’s “State of the Union” on Sunday.  

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