Russian attacks killed at least ten people across Ukraine, with officials saying that four of the deaths in Kharkiv happened in the most powerful Russian drone strike to hit the eastern city since the start of the war.
One of Ukraine's largest cities, Kharkiv is located just a few dozen kilometres from the Russian border and has been under constant Russian shelling during more than three years of war.
"Kharkiv is currently experiencing the most powerful attack since the start of the full-scale war," city mayor, Ihor Terekhov, said on the Telegram messenger.
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Dozens of explosions were heard in the city through the night and Russian troops were striking simultaneously with missiles, drones and guided aerial bombs, he said.
Meanwhile, a large-scale prisoner exchange between Russia and Ukraine was thrown into doubt after both sides accused each other of delaying and thwarting the swap.
At talks in Istanbul on Monday, Russia and Ukraine agreed to release all wounded soldiers and those aged under 25 who had been captured - more than 1,000 people on each side.
Russia said it would also hand back the remains of 6,000 killed Ukrainian soldiers.
Russia yesterday accused Ukraine of not turning up to collect the bodies and not agreeing a date to swap the captured soldiers, while Ukraine claimed Russia was playing "dirty games" by not sticking to the agreed parameters for the exchange.
"The Ukrainian side has unexpectedly postponed for an indefinite period both the acceptance of the bodies and the exchange of prisoners of war," Russia's top negotiator Vladimir Medinsky said on social media.
A defence ministry spokesman said "the Ukrainian side is still refraining from setting a date" for the first stage of the prisoner swap.
'Dirty games'
The exchange was set to be the largest of the war, topping last month's 1,000-for-1,000 swap that was agreed at a first round of peace talks in Istanbul.
After the Istanbul talks, Ukrainian President Volodymyr Zelensky said it would take place this weekend, while Russia said it was ready for Saturday, Sunday or Monday.
Responding to Russia's accusations, Ukraine's Coordination Headquarters for the Treatment of Prisoners of War said no date had been agreed for the return of bodies.
It also said a list of names Russia said would be released did not match the terms of the agreement.
"Unfortunately, instead of constructive dialogue, we are again faced with manipulations," it said in a statement on social media.
"We call on the Russian side to stop playing dirty games and return to constructive work to bring people back to both sides and to clearly implement the agreement in the coming days," it added.
The spat came as Russia launched a massive aerial attack across Ukraine, heavily targeting the city of Kharkiv overnight and throughout the day.
Mr Zelensky urged Ukraine's Western backers to heap more "pressure" on Russia, with at least ten people killed in the barrage.
'Powerful attack'
Four people were killed and more than 60, including a baby, were wounded in Kharkiv as homes and apartment blocks were pummelled overnight and guided bombs were dropped on the city on this afternoon.
Three people were also killed in the frontline Donetsk region, which has seen the most intense fighting of the war, and three more in the Kherson region, also partially occupied by Moscow's forces.
Since Russia invaded in February 2022, tens of thousands have been killed, with millions forced to flee their homes as cities and villages across eastern Ukraine have been destroyed.
The Ukrainian air force said Russia had fired 206 drones and nine missiles in the overnight barrage.
Russia's defence ministry said it had launched a "group strike" against "military-industrial" facilities in Ukraine.
Despite talks, the two sides have made no progress towards halting the fighting.
Russian President Vladimir Putin has issued a host of sweeping demands on Ukraine as preconditions to a truce.
They include completely pulling troops out of four regions claimed by Russia, but which its army does not fully control, an end to Western military support and a ban on Ukraine joining NATO.
Mr Zelensky has rejected them as "old ultimatums" and repeated his call for sanctions on Russia.
"The Russians are preparing to continue the war, ignoring all peace proposals. They must be held accountable for this," he said in his evening address.
"Pressure forced Russia to enter the negotiation process. Pressure can force Russia to become realistic in the negotiation process," he added.
