Russian President Vladimir Putin on Monday declared a unilateral three-day ceasefire in Ukraine next month, a move met with skepticism by Ukrainian officials who demanded the Kremlin leader immediately accept a longer truce proposal from the United States that he has so far rejected.

The Kremlin said on Monday that President Vladimir V. Putin had ordered a three-day cease-fire in Ukraine next month, the second time in two weeks that Russia’s leader has promised a temporary pause in the fighting as President Trump shows growing impatience with his refusal to stop the war.