The Russian defence ministry claimed Ukraine had not abided by its own ceasefire, saying that air defences shot down 53 Ukrainian drones over Russian regions, the illegally annexed Crimean Peninsula and the Black Sea between Tuesday evening and dawn on Wednesday.
Five people were killed by a Ukrainian drone strike on the city of Dzhankoi in Crimea, according to Russia-installed governor Sergei Aksyonov.
He reported the casualties just after midnight, but posted about the attack itself more than 90 minutes earlier.
There had been no official sign from Moscow that it would heed Kyiv's ceasefire, and there was little hope for a pause in hostilities as the war stretches into its fifth year following Russia's all-out invasion of its neighbor.
US-led diplomatic efforts to stop the war in the past year have come to nothing.
On Tuesday, Russian drone and missile strikes on Ukraine killed 27 people and wounded 120 others, all of them civilians, according to Ukrainian Interior Minister Ihor Klymenko.
The war has killed more than 15,000 civilians, according to the United Nations.
"After yesterday's savage strikes against our cities and communities … the Russian army continued active hostilities and terrorist shelling throughout this day as well," Ukrainian President Volodymyr Zelenskiy said on X.
"Russia's choice is an obvious spurning of a ceasefire and of saving lives."
Despite Kyiv's open-ended suspension of hostilities, Russia has continued shelling, with aerial strikes using drones and powerful glide bombs, and has attempted to break through Ukrainian defences on the front line, Zelenskiy said.
"Russia must end the war it is currently waging," he said, urging Moscow to call off its invasion.
"The Russian side has our diplomatic proposals, and the only thing needed is Russia's willingness to move toward real peace."
Both sides have kept up long-range strike campaigns. On the roughly 1250km front line, meanwhile, Russia's bigger army remains engaged in a slow-moving and costly slog against Ukraine's drone-heavy defences.
Zelenskiy had announced the unilateral ceasefire after Russia said it would hold its own pause of hostilities over two days later this week while it marks the 81st anniversary of the defeat of Nazi Germany in World War II.
The Ukrainian leader said any breach of the ceasefire would trigger a military response.
European officials had welcomed Ukraine's unilateral move as a goodwill gesture illustrating its readiness for a peace settlement.
Russian forces launched 108 drones and three missiles overnight, Ukrainian Foreign Minister Andrii Sybiha said, with attacks continuing throughout the night and into Wednesday morning.
"Moscow once again ignored a realistic and fair call to end hostilities, supported by other states and international organisations," Sybiha said in a post on X.
Moscow's proposal to stop fighting on Friday and Saturday follows a pattern of Russia declaring short unilateral ceasefires during the war timed to coincide with various holidays, most recently Orthodox Easter.
Those suspensions of combat do not produce any tangible results amid deep mistrust between the warring sides.
Sybiha said Russia's actions exposed its calls for a separate ceasefire around May 9 as insincere.
"Putin only cares about military parades, not human lives," he said.
The diplomat called for increased international pressure on Moscow, including new sanctions, diplomatic isolation, accountability measures for war crimes and expanded military and civilian support for Ukraine.