Updated 10.37am
The Polish, Czech and Slovenian prime ministers were travelling to Kyiv by train on Tuesday in the first visit by foreign leaders to Ukraine's besieged capital since Russia invaded last month.
The visit comes as Russia pummels targets across Ukraine including Kyiv, which has nearly been encircled by Moscow troops, and as Russia and Ukraine are due to resume talks to end the nearly three-week war.
Mateusz Morawiecki, Petr Fiala and Janez Jansa are visiting as "representatives" of the European Union and are due to meet with Ukrainian President Volodymyr Zelensky, the Polish government said in a statement.
"In such crucial times for the world, it is our duty to be in the place where history is being made," Morawiecki said in a Facebook post.
"Because this is not about us, it is about the future of our children who deserve to live in a world free from tyranny," he said.
The government statement said that the visit had been organised "in agreement" with European Council chief Charles Michel and European Commission president Ursula von der Leyen.
"The purpose of the visit is to confirm the unequivocal support of the entire European Union for the sovereignty and independence of Ukraine and to present a broad package of support for the Ukrainian state and society," the statement said.
Top Polish government official Michal Dworczyk said the train crossed into Ukraine at around 0730 GMT.
The trio is accompanied by Jaroslaw Kaczynski, leader of Poland's populist right-wing Law and Justice (PiS) party, and will also meet Ukrainian Prime Minister Denis Shmyhal.
"Europe must send a strong signal for peace!" Polish government spokesman Piotr Muller tweeted.
Kyiv suffers heavy overnight bombing, curfew imposed
A series of powerful explosions rocked residential districts of Kyiv early Tuesday killing two people, just hours before talks between Ukraine and Russia were set to resume.
At least three large blasts were heard from the centre of the capital, sending columns of smoke high into the sky.
As dawn broke the damage became clear, with one strike hitting a large 16-storey housing block.
There, a fire raged and smoke billowed from the charred husk of the building, as emergency services and stunned locals navigated an obstacle course of glass, metal and other debris littering the road.
"The bodies of two people were recovered, 27 people were rescued," Ukraine's emergency service said.
Another residential building in the Podilsk area also came under attack.
Ukrainian MP Lesia Vasylenko posted a photo of a fire crew extinguishing a smouldering fire there -- the building's facade transformed into a mess of bent and tangled window frames and precariously dangling air conditioning units.
Vasylenko said the district had been "a place to get coffee and enjoy life. Not anymore. Explosive hit just 30 minutes ago."
Just hours earlier, Ukrainian President Volodymyr Zelensky -- wearing his now-signature military-green crew neck -- issued a new video address sounding a note of cautious optimism about ongoing peace talks.
He claimed Russia was beginning to realise victory would not come on the battlefield.
"They have already begun to understand that they will not achieve anything by war," Zelensky said.]
The two sides are still far apart in the negotiations, with Moscow demanding Ukraine turn away from the West and recognise Moscow-backed breakaway regions.
Ukrainian negotiators say they want "peace, an immediate ceasefire and the withdrawal of Russian troops".
Kyiv is surrounded to the north and east and nearly half its population of three million people have fled. Only roads to the south remain open, city authorities have set up checkpoints and residents are stockpiling food and medicine.
On Tuesday morning, Mayor Vitali Klitschko said Kyiv will impose a 36-hour curfew from Tuesday night amid a "difficult and dangerous moment" after several Russian strikes.
"Today is a difficult and dangerous moment," former boxing champion Klitschko said in a statement, adding that the curfew will last from 8 pm on Tuesday until 7 am on Thursday.