Top Russian military brass held talks on when and how the Kremlin might use a tactical nuclear weapon in Ukraine, multiple US outlets reported, causing consternation amongst Kyiv's western allies.
It is unclear whether Russian President Vladimir Putin participated in the discussions.
Washington has "grown increasingly concerned" about a potential Russian nuclear strike on Ukraine, the White House stated.
"We still have not seen any indication that the Russians are making preparations for such use... But this is all deeply concerning to us," spokesman for the National Security Council John Kirby said on Wednesday.
"We have grown increasingly concerned about the potential as these months have gone on," Kirby added.
Putin recently denied having any intentions of using nuclear weapons in Ukraine but described the conflict there as part of alleged efforts by the West to secure its global domination, which he insisted are doomed to fail.
Speaking in late October at the Valdai discussion club meeting -- a state-funded conference of international foreign policy experts -- Putin said it is pointless for Russia to strike Ukraine with nuclear weapons.
Putin said an earlier warning of his readiness to use "all means available to protect Russia" did not amount to nuclear sabre-rattling but was merely a response to Western statements about their possible use of nuclear weapons.
"We have maintained, I believe, an appropriate level of concern about the potential use of weapons of mass destruction in Ukraine to include nuclear weapons," Kirby told reporters
In recent weeks, Moscow has amped up its claims that Kyiv is preparing a nuclear "dirty bomb" attack, with Defence Minister Sergei Shoigu said to have made calls to his western counterparts to
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