This is according to CNN, citing two European officials who spoke on the condition of anonymity.
It said this means a significant review of US estimates, who earlier expected the Russian military operation to be over quickly, TASS reported.
Russian President Vladimir Putin said in a televised address on February 24 that in response to a request by the heads of the Donbass republics he had made a decision to carry out a "special military operation" in Ukraine.
The Russian leader stressed that Moscow had no plans of occupying Ukrainian territories, noting that the operation was aimed at the denazification and demilitarization of Ukraine.