The Kremlin on Thursday refused to give any details about a cautionary message delivered by the director of the CIA to Moscow this week about the consequences of any Russian nuclear strike on Ukraine.
Central Intelligence Agency Director William Burns warned Sergei Naryshkin, head of Russia's SVR foreign intelligence service, about the consequences of any use of nuclear weapons, a White House official said.
It was the first known high-level, face-to-face U.S.-Russian contact since Russia invaded Ukraine in February.
"We are not saying anything about the content of the negotiations," Kremlin spokesman Dmitry Peskov told reporters when asked about the meeting.
Russia's deputy foreign minister, Sergei Ryabkov, said only that the "questions discussed there were of a sensitive nature" and that Washington had requested the meeting. The SVR did not respond to a request for comment.
After the meeting, Burns then visited Kyiv and met Ukrainian President Volodymyr Zelenskiy. Zelenskiy said the CIA director had spent time in a bomb shelter before the two men met amid Russian missile strikes.
Burns, a former U.S. ambassador to Russia, was sent to Moscow in November 2021 by President Joe Biden to caution Putin about his troop build-up around Ukraine, which preceded the Russian leader's invasion four months later.
The invasion has triggered the biggest confrontation between Moscow and the West since the 1962 Cuban Missile Crisis.
NUCLEAR ESCALATION?
Concerns about a nuclear escalation have focused on how Putin would react to a catastrophic defeat of Russian forces in Ukraine and on how Russia might defend Ukrainian territory which it says it has annexed.
Putin has said Russia will defend its territory with all available means, including nuclear weapons, if attacked.
But Russian officials say the West has repeatedly misinterpreted Kremlin statements and that the circumstances in which it might use such weapons are clearly set out in its nuclear doctrine.
Asked if it was possible that Russia would use a nuclear weapon and whether or not it had been discussed, Kremlin spokesman Dmitry Peskov said on Thursday that even the framing of such questions was unacceptable.
"If you have noticed, no one from the Russian side is discussing this topic and has not discussed it," Peskov said.
He blamed European capitals for discussing the nuclear issue and "thereby escalating tensions in a completely unacceptable, impermissible and potentially dangerous sphere."
Russia and the United States are by far the biggest nuclear powers, together holding around 90% of the world's nuclear warheads - enough to destroy the planet many times over.
(Reporting by Guy FaulconbridgeEditing by Andrew Osborn)
