There have been reports of Russian troops firing as civilians attempt to flee besieged cities, despite Ukraine and Russia agreeing in principle to the opening of six escape corridors on Wednesday.
In the village of Demydiv, about 25 kilometres north of the capital Kiev, Russian troops fired on Ukrainian police officers, according to security forces. One policeman was killed and another seriously injured. In addition, a civilian was taken to hospital with serious injuries, officials said.
Hundreds of thousands of civilians in the port city of Mariupol in particular were hoping to be rescued from desperate conditions there, but the agreed corridor has still not become operational, according to separatists in the Donetsk region.
"People are leaving Mariupol themselves as soon as possible," the spokesperson for the pro-Russian forces, Eduard Bassurin, told Russian state television, adding that 42 people had been able to leave the city on the Sea of Azov on Tuesday.
Ukrainian Foreign Minister Dmytro Kuleba tweeted: "Russia continues to hold more than 400,000 people hostage in Mariupol, blocking humanitarian aid and evacuation."
Other safe corridors from the embattled towns of Enerhodar, Volnovakha, Izyum and Sumy, as well as several towns north of Kiev, were also planned, with the evacuation of civilians from the north-eastern city of Sumy set to enter its second day on Wednesday.
According to the Ukrainian government, 6,700 people have already been rescued from Sumy, which was the only one of five agreed-upon escape corridors to function on Tuesday.
According to the head of the regional administration, Dmytro Shyvytskyy, the death toll from Monday night's heavy airstrikes on Sumy rose to 22, including three children.
The body of a boy was found under the rubble on Tuesday. A bomb had hit a private house, killing nine people there, Shyvytskyy wrote.
Elsewhere in Ukraine, there were renewed concerns about the safety of the former Chernobyl nuclear power plant on Wednesday after it emerged its electricity supply was cut off by fighting.
According to the International Atomic Energy Agency (IAEA), 210 technicians and local safety staff have been on duty continuously at Chernobyl for almost two weeks, as there has been no shift change since Russian forces took control of the facility.
Some 14,500 people have travelled to Ukraine to join the fight against the Russian invasion in the past few days, according to the Ukrainian military.
Around 12,000 of them were Ukrainians living abroad who wanted to join the national defence effort, according to the army. Others were foreign volunteers who planned to join the country's international legion.
In a statement, Ukraine's general staff put the current death toll for Russian forces at over 12,000 soldiers. While it hasn't released any recent figures, Russia said a few days ago that it had lost fewer than 500 soldiers in the conflict so far.
The Polish government appeared to row back on its proposal to send MiG-29 fighter jets to Ukraine on Wednesday, after the plan was dismissed as "untenable" by Washington.
Prime Minister Mateusz Morawiecki said on Wednesday that the decision to make such a transfer would have to be made by NATO rather than Poland.
"We are grateful to Poland ... for its willingness to hand over fighter jets to Ukraine. The only problem is logistics," Ukrainian President Volodymyr Zelensky said in a video message released on Wednesday, adding "This must be solved! Immediately."
Russian Foreign Minister Sergei Lavrov and his Ukrainian counterpart Dmytro Kuleba are due to meet in the Turkish city of Antalya on Thursday, in what are to be the highest level talks between the two sides since the Russian invasion began two weeks ago.
Ahead of the meeting, Russia's Foreign Ministry spokesperson Maria Zakharova denied that regime change was Moscow's ultimate goal in Ukraine.
"The goals of the special military operation are to protect the Donetsk and Luhansk people's republics, demilitarize and denazify Ukraine and eliminate the military threat to Russia," Zakharova said.
