Czech Prime Minister Petr Fiala and Poland's Mateusz Morawiecki announced plans for the visit, saying they and Slovenia's Janez Jansa would meet Ukraine's President Volodymyr Zelenskiy on Tuesday. Zelenskiy's office confirmed the plans.

"The purpose of the visit is to confirm the unequivocal support of the entire European Union for the sovereignty and independence of Ukraine," Fiala said, adding the three leaders would present a broad support package for Ukraine.

Morawiecki's aide, Michal Dwoczyk, told reporters the delegation had crossed the Polish-Ukraine border and was heading to Kyiv by train, in what the Polish leader said was a historic mission.

"It is our duty to be where history is forged. Because it's not about us, but about the future of our children who deserve to live in a world free from tyranny," Morawiecki said.

The three leaders will arrive in a city that is still under bombardment, where around half of the 3.4 million population has fled and many are spending nights sheltering in underground stations. Two powerful explosions rocked the capital before dawn on Tuesday, and emergency services said two people died when an apartment building was struck.

Nearly three weeks into a war which Western countries say Moscow believed it would win within days, Europe's biggest invasion force since World War II has been halted at the gates of Kyiv.

Armoured columns of Russian forces have failed to capture any of Ukraine's 10 biggest cities, despite bombardment that has reduced some residential areas to rubble.

Hosting foreign dignitaries in his own capital would be a remarkable symbolic success for Zelenskiy, who rejected offers to evacuate early in the war, staying under bombardment to rally his nation with nightly messages from inside the city.

In his most confident public statement yet, Zelenskiy called on Russian forces to surrender, saying they and their officers already knew that the war was hopeless.

"Russian conscripts! Listen to me very carefully. Russian officers! You've already understood everything: You will not take anything from Ukraine. You will take lives. There are a lot of you. But your life will also be taken. But why should you die? What for? I know that you want to survive," he said.

One of Zelenskiy's top aides said the war would be over by May - and could even end within weeks - as Russia had effectively run out of fresh troops to keep fighting.

"We are at a fork in the road now: there will either be a peace deal struck very quickly, within a week or two, with troop withdrawal and everything, or there will be an attempt to scrape together some, say, Syrians for a round two and, when we grind them too, an agreement by mid-April or late April," Oleksiy Arestovich said in a video.

Russia says it is not targeting civilians and is carrying out a "special operation" to disarm and "denazify" Ukraine, which Kyiv and its allies call a baseless pretext to invade a democratic nation of 44 million people.

In the city of Rivne in western Ukraine, hundreds of miles from the combat zone, Ukrainian officials said 19 people had been killed in a Russian air strike on a television tower. If confirmed, that would be by far the worst attack so far on a civilian target in the northwestern half of the country.

Ukrainian and Russian delegations were due to resume peace talks later on Tuesday by video link.

So far no progress has been announced at those talks, which have focused on allowing civilians to evacuate and bring aid to surrounded cities, especially the eastern port of Mariupol.

Hundreds of people are believed to have been killed there since Russia laid siege to the city of 400,000 in the war's first week. Russian troops permitted a first column of cars to leave the city on Monday but attempts to enact a local ceasefire to bring in aid convoys have failed for 10 straight days.

In an intelligence update on Tuesday, Britain's ministry of defence reported demonstrations against Russian occupation in the cities of Kherson, Berdyansk and Melitopol, with Russian troops firing warning shots to disperse crowds in Kherson.

Australian Associated Press