Russian forces have encountered strong resistance from Ukraine defenders, and US officials say they believe the invasion has been more difficult, and slower, than the Kremlin envisioned, though that could change as Moscow adapts.

A senior US intelligence official says Belarus is expected to send troops into Ukraine as soon as Monday to fight alongside Russian forces that invaded Ukraine last week. Belarus has been providing support for Russia's war effort, but so far has not taken a direct part in the conflict.

The American official has direct knowledge of current US intelligence assessments and says the decision by Belarus' leader on whether to bring Belarus further into the war depends on talks between Russia and Ukraine happening in the coming days. The official spoke anonymously to discuss the sensitive information.

Russian forces have encountered strong resistance from Ukraine defenders, and US officials say they believe the invasion has been more difficult, and slower, than the Kremlin envisioned, though that could change as Moscow adapts.