President Zelenskyy has said peace talks with Russia now “sound more realistic” but time is still needed to secure a deal in Ukraine’s interests.
A Ukrainian negotiator also sounded cautiously optimistic after the latest meeting, saying “there is certainly room for compromise” despite “fundamental contradictions”.
It comes as a flurry of Russian attacks probed closer into central Kyiv on Tuesday, with a huge fire breaking out in a 15-storey apartment building in the west of the capital.
“Everyone should work, including our representatives, our delegation, for negotiations with the Russian Federation,” said Mr Zelenskyy in his nightly address.
“It is difficult, but important, as any war ends with an agreement.
“The meetings continue, and, I am informed, the positions during the negotiations already sound more realistic. But time is still needed for the decisions to be in the interests of Ukraine.”
Ukraine war live: Latest developments
Mr Zelenskyy has also hinted he may accept security guarantees that stop short of joining NATO. Ukraine abandoning its ambitions to join the military alliance is among Russian demands.
In other developments
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• Zelenskyy to address US Congress later, as NATO defence ministers meet in Brussels
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• Journalist who protested live on Russian TV is fined £210
• More than 122,000 Britons have now registered interest for refugee scheme
The leaders of Poland, Slovenia and Czech Republic have arrived in Kyiv after taking a train to meet the president – a bold show of support given the risks involved.
Polish President Mateusz Morawiecki tweeted a picture of the the group, saying: “Europe must understand that if it loses Ukraine it will never be the same again.
“It will no longer be Europe. Rather it will be a defeated, humiliated and pathetic version of its former self.”
A curfew is also now in force in Kyiv until to 7am (5am GMT) on Thursday after a ratcheting up of strikes over the past 48 hours.
Mayor Vitali Klitschko urged his fellow citizens to “spend the time in the bunkers” as he visited the aftermath of the latest attack in the Svyatoshynskyi district.
His brother, Wladimir, told Sky News: “It doesn’t matter who you are on the Ukrainian soil now… if you have a press badge, or you’re a little girl or boy, an adult, man or woman… or an old person… you are a target from Russia, from the Russian army.”
In the southern city of Mariupol – which has been pummelled for several weeks – 20,000 people used 4,000 private cars to escape on Tuesday as a humanitarian corridor operated for a second day.
However, Ukrainian authorities have accused Russia of blocking aid supplies to the cut-off city.
Russian troops have also seized a hospital in Mariupol and taken around 500 people hostage, according to regional leader Pavlo Kyrylenko.
He said Russian forces had driven 400 people from neighbouring houses into Regional Intensive Care Hospital, where they joined around 100 doctors and patients inside.
The troops are using those inside the hospital as human shields and not allowing anyone to leave, he said on messaging app Telegram.
Another 8,533 people were also evacuated from the northeast Sumy region on Tuesday, according to deputy prime minister Iryna Vereshchuk.
Meanwhile, Ukrainian forces pushed back an attempt to storm the second-biggest city of Kharkiv on Tuesday evening, said the head of the region.
Oleh Synehubov called it a “shameful defeat” and said the attackers were pushed back beyond their previous position in the Piatykhatky suburb, nine miles north.
There is no word yet on casualties, but shelling of the eastern city is said to have intensified after dark. It came after 60 missiles hit the city’s historical centre the night before.
Russia has met fierce resistance since the invasion began about three weeks ago and the number of soldiers killed means it is likely “struggling”, according to the UK Ministry of Defence.
In its latest assessment, it said the Kremlin appears to be increasingly trying to replace lost soldiers to keep its plans on track.
“Russia is redeploying forces from as far afield as its Eastern Military District, Pacific Fleet and Armenia, the MoD tweeted.
“It is also increasingly seeking to exploit irregular sources such as Private Military Companies, Syrian and other mercenaries.
“Russia will likely attempt to use these forces to hold captured territory and free up its combat power to renew stalled offensive operations.”