Imposing a deadline on a negotiation for a deal you desperately want is a risky tactic if your only move is to walk away from a deal you desperately want.

Many of the elements of the U.S. proposal would be politically damaging to Zelensky, creating an opening Moscow could exploit, say analysts and officials.

The Kremlin said on Wednesday that countries involved in peace talks around Ukraine still needed to narrow their differences and that there were "a lot of nuances" that needed to be worked out before any deal could be reached.