US National Security Adviser Jake Sullivan has held undisclosed talks with top Russian officials in hopes of reducing the risk of the war in Ukraine spilling over or worsening into nuclear conflict, a report said on Sunday.
The Wall Street Journal quoted US and allied officials as saying that Mr Sullivan held confidential talks in recent months with Kremlin aide Yuri Ushakov and Russian Security Council secretary Nikolai Patrushev that were not disclosed publicly.
The White House declined to comment on the report.
"People claim a lot of things," National Security Council spokeswoman Adrienne Watson said.
The officials did not provide the dates or the number of calls, the paper said. A peace settlement was not a goal of the discussions, it said.
Few high-level contacts between US and Russian officials have been made public in recent months as Washington has insisted that any talks on ending the war in Ukraine be held between Moscow and Kyiv.
The reported conversations took place as the West has accused Moscow of increasing nuclear talk, most recently by repeatedly accusing Kyiv of planning to use a radioactive "dirty bomb", without offering evidence.
Kyiv has denied having such a plan and the US and other western nations have said Russia could be planning to orchestrate such an attack itself and use it as a pretext to escalate the conflict.
Russia in turn has accused the West of "encouraging provocations".
Mr Sullivan travelled to Kyiv on Friday and pledged Washington's "unwavering and unflinching" support for Ukraine.