Ukraine has praised the courage of three European leaders who made a long, hazardous journey by rail from Poland to Kyiv in a show of support as the city came under further Russian attack.

The prime ministers of Poland, Slovenia and the Czech Republic met Ukraine's President Volodymyr Zelensky on Tuesday evening as a curfew began in Kyiv.

Afterwards, the Czech leader told Ukrainians that they were "not alone".

They are the first Western leaders to visit Ukraine since Russia invaded.

"We admire your brave fight," Petr Fiala wrote in a tweet. "We know that you're also fighting for our lives. You're not alone, our countries stand by your side."

"Your visit is a powerful expression of support for Ukraine," Mr Zelensky is quoted as telling the group.

On Wednesday, Poland's Mateusz Morawiecki tweeted that Ukraine was reminding Europe what courage was. It was time for "sluggish and decayed" Europe to reawaken and "break through her wall of indifference and give Ukraine hope", he said.

The leaders had arrived back in Poland on Wednesday morning, a Polish government spokesperson said.

Also on the trip was Jaroslaw Kaczynski, the head of Poland's ruling party, and he called for the creation of a Nato or international peacekeeping mission that "will also be able to defend itself and operate in Ukraine".

However, one of his advisers later clarified that Mr Kaczynski had not been calling for Nato to get involved militarily.

"Here the position is unchanged. Neither Poland nor Nato are taking, or will take part, in the war," Michal Dworczyk told Polish Radio.

Ukraine's Prime Minister Denys Shmyhal wrote on Twitter that "devastating" sanctions against Russia had been discussed during the meeting in Kyiv, including the "recognition of Russia as a sponsor of terrorism".

As the talks took place on Tuesday evening, loud explosions could be heard from fighting on the western edge of the capital city.

The European Union said the politicians were not carrying any particular mandate, but that leaders in Brussels were aware of the trip, as it was mentioned during an informal EU summit in Versailles, France, last week.

Poland's Deputy Foreign Minister Marcin Przydacz admitted the trip was risky, but said it was "worth taking for the sake of values". He said they had told the Russians the visit was taking place.

All three leaders on the trip to Kyiv have been vocal supporters of Ukraine in recent weeks. Slovenia's prime minister said last week that the EU should send a strong message that Ukraine will eventually be granted membership.

Czech Foreign Minister Jan Lipavsky said the visit was a strong and important gesture to show solidarity with Ukraine.

"Ukraine's security is European security; therefore we need to do everything possible to help them survive this sickening barbaric Russian attack," he told the BBC.

The leaders decided to travel by train because flying by Polish military jet could have been viewed by Russia as dangerously provocative, BBC Europe editor Katya Adler reports.

Ukraine's president has repeatedly called on Nato to impose a no-fly zone over his country's airspace, but Nato has refused.

Mr Zelensky said Ukrainians now understood they could not join Nato: "We have heard for years that the doors were open, but we also heard that we could not join. It's a truth and it must be recognised. I am glad that our people are beginning to understand this and rely on themselves and our partners who help us."

The city was facing a difficult and dangerous moment, he said: "This is why I ask all Kyivites to get prepared to stay at home for two days, or if the sirens go off, in the shelters."