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.

"Our position remains unchanged: we want to see an end to the war... It must be principled, consistent and firmly based on the UN Charter, international law and all relevant resolutions," he said, stressing the importance of a long-term peace settlement that includes recognition of Ukraine's sovereignty and territorial integrity.

Russian President Vladimir Putin on Monday declared a unilateral ceasefire in Ukraine from May 8 to May 10, but Ukraine and the United States reacted cautiously. The Russian mini-truce would coincide with the 80th anniversary of victory over Nazi Germany in World War II.