Ukraine says Russia has stepped up its attacks despite the "Easter truce" it declared, while the Kremlin claims Kyiv has broken the ceasefire more than a thousand times.
President Volodymyr Zelenskyy said either "Putin does not have full control over his army" or Russia has no intention of trying to end the war, in a social media post on X.
His comments came after Russia's defence ministry claimed Ukraine had broken President Vladimir Putin's ceasefire more than a thousand times, Russian news agencies reported.
Mr Putin announced a surprise one-day ceasefire in Ukraine on Saturday for Easter.
The US State Department said it would support the ceasefire's extension beyond Sunday.
But Russia's TASS news agency later said Mr Putin had not given any further order to extend the ceasefire beyond 9pm on Sunday, local time.
But the Kremlin said the border districts of the Bryansk, Kursk and Belgorod regions had since been attacked, causing civilian deaths and injuries.
Several blasts had also ripped through a Russian-controlled city in eastern Ukraine on Sunday local time, according to a Russian news agency.
At least three blasts were heard in the city of Donetsk, which has been under Russia's control since 2014, according to the TASS state news agency.
Reuters said it could not immediately independently verify these battlefield reports.
A 'pretence' of a pause
Meanwhile Kyiv said Russian forces had continued artillery fire.
Ukrainian President Volodymyr Zelenskyy said earlier Sunday local time that the Russian army was making a pretence of a pause in hostilities, continuing overnight attempts to inflict frontline losses on Ukraine.
Mr Zelenskyy urged Ukrainians not to give up hope that peace would return to their country and to persevere to overcome the three-year war.
"In those who stand next to you. In Ukrainian men, in Ukrainian women. Faith that evil may have its hour but God will have his day," he said.
"We know what we are defending. We know what we are fighting for. For whom and for whose sake.
"The day of life will come. The day of peace. The day of Ukraine. A day that lasts a century. And we will be able to gather together again. At one table. On a peaceful Easter."
Early on Sunday, Ukrainian forces reported 59 instances of shelling and five assault attempts along the front line, Mr Zelenskyy added.
Ukraine's military confirmed activity on the front line had decreased, but the fighting had not stopped.
"It is decreasing, but it hasn't disappeared," Viktor Trehubov, a military spokesperson for Ukraine's eastern front, told the national television.
"To be honest, we didn't hold out much hope that this would actually happen."
Trump's peace push
The ceasefire followed a US announcement that it could abandon peace talks in "a matter of days" unless Moscow and Kyiv showed they were serious about negotiating.
US President Donald Trump has vowed to bring a swift end to the war, while shifting US policy from firmly supporting Kyiv towards accepting Moscow's account of the conflict.
On Sunday, the US State Department said it would support an extension of the ceasefire.
"We have seen President Putin's announcement of a temporary ceasefire due to Easter. We remain committed to achieving a full and comprehensive ceasefire," a State Department spokesperson said in an emailed statement on Sunday.
"As we assess their seriousness in this instance, we would welcome it extending beyond Sunday."
Last month, after Ukraine accepted Mr Trump's proposal for a 30-day truce but Moscow rejected it, the sides agreed only to limited pauses of attacks, which each accused the other of breaking.
Mr Zelenskyy reiterated that Kyiv was willing to extend the ceasefire for 30 days but said if Russia kept fighting on Sunday, so would Ukraine.
"Ukraine will continue to act in a mirror manner," he said.
The European Union reacted cautiously to Mr Putin's ceasefire declaration, saying Moscow could stop the war immediately if it wanted to.
Easter falls on the same day this year for Orthodox and Western churches, and Mr Zelenskyy urged Ukrainians in an Easter message not to give up hope that peace will return to their country.
"We know what we are defending. We know what we are fighting for. For whom and for whose sake," he said.
Reuters
