Ukraine's forces reported 2,935 violations of Russia's own Easter ceasefire vow, President Volodymyr Zelensky said early on Monday.
"The nature of Ukrainian actions will continue to be mirrored: we will respond to silence with silence, our strikes will be to protect against Russian strikes," Zelensky said in a post on Telegram.
In contrast, Russia's defense ministry claimed on Sunday that Ukraine had broken the Easter ceasefire declared by Russian President Vladimir Putin more than a thousand times, inflicting damage to infrastructure and causing civilian deaths.
The ministry said that Ukrainian forces had shot at Russian positions 444 times, while it had counted more than 900 Ukrainian drone attacks. It also said the border districts of the Bryansk, Kursk, and Belgorod regions have been attacked.
Putin, who ordered thousands of Russian troops into Ukraine in February 2022, ordered Russian forces to "stop all military activity" along the front line in the three-year-old war until midnight Moscow time (2100 GMT) on Sunday.
Zelensky said Russia was pretending to observe the Easter ceasefire, but had in fact continued hundreds of artillery attacks on Saturday night, with more assaults on Sunday.
Zelensky wrote on the X social media platform that Russia had launched 26 assaults from midnight until midday local time (0900 GMT).
Zelensky's statements
"Either Putin does not have full control over his army, or the situation proves that in Russia, they have no intention of making a genuine move toward ending the war, and are only interested in favourable PR coverage," Zelensky's post said.
Earlier he said the Russian army "is trying to create a general impression of a ceasefire", while continuing to inflict losses on Ukraine's front line.
Ukraine's military said earlier on Sunday that activity on the front line had decreased. Some Russian military bloggers also said military activity along the frontline has substantially decreased.
Reuters was unable to immediately verify the battlefield reports from either side.
The US will walk away from efforts to broker a peace deal unless there are clear signs of progress soon, US President Donald Trump and his secretary of state, Marco Rubio, said on Friday.
Trump's peace push
Trump, who says he wants to be remembered as a peacemaker, has repeatedly warned of the escalation risk of the war - which his administration now casts as a proxy conflict between the US and Russia, echoing Moscow's stance.
Last month, after Ukraine accepted Trump's proposal for a 30-day truce, Putin said crucial issues of verification had not been sorted out. Both Moscow and Kyiv have agreed to a moratorium on attacks on energy targets and at sea, which each accuses the other of breaking.
Zelensky reiterated that Kyiv was willing to extend the ceasefire for 30 days but said that if Russia kept fighting on Sunday, so would Ukraine.
Putin told his top general, Valery Gerasimov, to be ready to respond "in full" if Kyiv broke the truce.
Russia controls just under one-fifth of Ukraine, including Crimea, which Moscow annexed in 2014, and the regions of Luhansk, Donetsk, Zaporizhzhia, and Kherson.
Putin, when announcing the ceasefire before heading to an Orthodox Easter service, said the truce would show whether or not Ukraine was ready or able to implement peace. Putin thanked Trump, Chinese President Xi Jinping, and leaders from the BRICS group of emerging economies for their attempts to mediate.
Putin and Moscow Mayor Sergei Sobyanin joined other worshippers for an Easter service led by the head of Russia's Orthodox Church, Patriarch Kirill, a faithful backer of the Russian leader and an advocate for the war in Ukraine.
Putin and Sobyanin stood in Moscow's main church, the Cathedral of Christ the Saviour, while Kirill led a procession, and a video of the service was shown.
Reactions to Putin's ceasefire declaration
The European Union reacted cautiously to Putin's ceasefire declaration, saying Moscow could stop the war immediately if it wanted to.
UN spokesman Stephane Dujarric reiterated UN support "for meaningful efforts towards a just, lasting and comprehensive peace that fully upholds Ukraine's sovereignty, independence and territorial integrity."
Easter falls on the same day this year for Orthodox and Western churches, and Zelensky urged Ukrainians not to give up hope that peace will one day return.
"We know what we are defending. We know what we are fighting for," he said in a social media video, wearing a traditional Ukrainian embroidered shirt and standing in front of Kyiv's main church, Saint Sophia Cathedral.
The US State Department noted that it had seen Moscow's Saturday announcement, but that it was still seeking a permanent end to the hostilities.
"We have seen President Putin's announcement of a temporary ceasefire due to Easter. We remain committed to achieving a full and comprehensive ceasefire," the US State Department said in a statement emailed to Reuters.
"As we assess their seriousness in this instance, we would welcome it extending beyond Sunday."