Russia and US in 'very sporadic' talks over nuclear issues, Kremlin says

U.S. and Russian officials have been in "sporadic" contact about nuclear issues, the Kremlin said on Monday, one day after National Security Adviser Jake Sullivan warned of "catastrophic consequences" if Russia uses nuclear weapons. 

Russian President Vladimir Putin said last week that his country's nuclear threats are "not a bluff." 

"I want to remind you that our country also has various means of destruction," Putin said on Wednesday. "When the territorial integrity of our country is threatened, to protect Russia and our people, we will certainly use all the means at our disposal."

The threats have been condemned by top U.S. officials, with Sullivan saying on Sunday that the U.S. has communicated with Russia in private channels about the response America would take. 

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"If Russia crosses this line, there will be catastrophic consequences for Russia. The United States will respond decisively," Sullivan told NBC News on Sunday. 

Kremlin spokesman Dmitry Peskov said Monday that there are "channels for dialogue" that are of a "very sporadic nature," according to the Russian state-owned news outlet RIA Novosti. 

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Ukrainian President Volodymyr Zelenskyy accused Putin of using the weapons as "nuclear blackmail."

"Maybe yesterday it was a bluff. Now, it could be a reality," Zelenskyy told CBS on Sunday. "I don't think he's bluffing."