Ukraine war: President Zelenskyy says no-fly zone is needed to avert humanitarian catastrophe as thousands flee in ceasefire

Ukraine's President has said the international community will be responsible for a mass "humanitarian catastrophe" if it does not agree a no-fly zone to protect his country.

In a daily televised address, Volodymyr Zelenskyy said the threat level in Ukraine was at a maximum nearly two weeks into Russia's invasion, but Ukrainians had shown they would never give in.

"Russia uses missiles, aircraft and helicopters against us, against civilians, against our cities, against our infrastructure. It is the humanitarian duty of the world to respond," he said.

A temporary ceasefire to allow civilians to escape from besieged cities is in place in parts of Ukraine - despite Russia failing to honour pledges in previous days.

Ukrainian Deputy Prime Minister Iryna Vereshchuk said Ukraine will try to evacuate civilians through six "humanitarian corridors", including from the besieged southern port city of Mariupol.

She said in a video statement that Ukrainian armed forces had agreed to stop firing in those areas from 9am until 9pm (0700-1900 GMT) and urged Russian forces to fulfil their commitment to local ceasefires.

Ukraine war: 'Catastrophic' situation in Mariupol- follow live updates

She said the corridors that would open would go from Mariupol to Zaporizhzhia; Enerhodar to Zaporizhzhia; Sumy to Poltava; Izyum to Lozova; Volnovakha to Pokrovsk; and from several towns around Kyiv which she identified as Vorzel, Borodyanka, Bucha, Irpin and Hostomel to the capital.

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A convoy of evacuees left the city of Enerhodar in southern Ukraine on Wednesday, its mayor said in a statement on social media.

Enerhodar is the site of Europe's largest nuclear power station of its kind.

The Russian assault on the area raised alarm bells last week when parts of the plant's facility were set ablaze. The plant remains under Russian control.

Enerhodar Mayor Dmytro Orlov said "mostly women and children, the elderly, left the city."

Russia 'holding Mariupol hostage'

There are few other details about the new evacuation effort in other cities.

Mariupol, where nearly half of the population of 430,000 is hoping to flee, has been surrounded by Russian forces for days.

Corpses lie in the streets and people break into shops in search of food and melt snow for water. Thousands huddle in basements, sheltering from the Russian shells pounding this strategic port on the Azov Sea.

Ukrainian Foreign Minister Dmytro Kuleba accused Russia of holding residents of Mariupol hostage by continuing to shell the city.

"Almost 3,000 newborn babies lack medicine and food," he wrote on Twitter. "Russia continues holding hostage over 400,000 people in Mariupol, blocks humanitarian aid and evacuation. Indiscriminate shelling continues."

Orchestra plays in Kyiv square

In Kyiv air raid sirens repeatedly went off and explosions could be heard there, raising tensions in the rattled city.

But in an act of defiance on a Kyiv square, an orchestra assembled before a small crowd to play the national anthem as Russian forces advanced on the city.

The Kyiv-Classic Symphony Orchestra also played an excerpt from Beethoven's Ode to Joy, on which the European Union's anthem is based a nod to the Ukraine government's desire to move closer to Europe and away from Russia's orbit.

Dozens of people gathered to watch on the central Maidan Square, some waving Ukrainian flags. They applauded when the national anthem was finished and a woman cried out "To Ukraine!"

Shelling disrupts evacuation in Izyum

A planned evacuation of civilians from Izyum in the eastern Kharkiv region was held up by Russian shelling, regional governor Oleh Synehubov said in an online post.

"Buses are still waiting at the entrance to Izyum," he said, adding that negotiations with the Russians were under way with the support of the Red Cross.

Britain is sending more weapons to Ukraine to help in the defensive effort, the Defence Secretary has said.

Ben Wallace told MPs the Russians are "changing their tactics and so the Ukrainians need to too", with the UK exploring the possible donation of portable anti-air missiles.

He also confirmed the UK has delivered 3,615 anti-tank weapons, known as NLAWs, and will shortly be supplying a "small consignment" of Javelin anti-tank missiles.

Radiation leak risk after power cut at Chernobyl

Radioactive substances could be released from Ukraine's Chernobyl nuclear power plant because it cannot cool spent nuclear fuel after its power connection was severed, Ukraine's state-run nuclear company Energoatom has said.

It said fighting made it impossible to immediately repair the high-voltage power line to the plant, which was captured by Russian forces.

Energoatom said there were about 20,000 spent fuel assemblies at Chernobyl that could not be kept cool amid a power outage.

Their warming could lead to "the release of radioactive substances into the environment. The radioactive cloud could be carried by wind to other regions of Ukraine, Belarus, Russia, and Europe," it said in a statement.

Mr Kuleba said Russia must urgently observe a temporary ceasefire to allow repairs on the power line.

But the UN nuclear watchdog said the loss of power does not have any critical impact on safety.

Russia says its operation is going to plan

Russia will achieve its goal of ensuring Ukraine's neutral status and would prefer to do that through talks, Russian foreign ministry spokeswoman Maria Zakharova said.

She told a briefing, Moscow's aims do not include overthrowing the Kyiv government and it hopes to achieve more significant progress in the next round of talks with Ukraine, adding that Russia's military operation was going strictly in line with its plan.

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She also called for the United States to explain to the world why it was supporting what Moscow cast as a military biological programme in Ukraine.

Last week, offering no evidence, foreign minister Sergei Lavrov said Russia had information that the US was worried about the prospect of losing control over what he described as chemical and biological laboratories in Ukraine and accused Britain of building military bases there.

The allegation is denied by Kyiv and the Pentagon.