Rescuers are searching for survivors in the ruins of a theatre ripped apart by a Russian air strike in the besieged Ukrainian city of Mariupol, authorities said.

Hundreds of civilians had been living in the grand, columned theatre in central Mariupol after their homes were destroyed in three weeks of fighting in the strategic port city.

Nearly a day after the attack, there were no reports of deaths.

With intense street fighting cutting off much of the city from the flow of information, there were also conflicting reports about whether survivors had emerged from the rubble.

“We hope and we think that some people who stayed in the shelter under the theatre could survive,” Petro Andrushchenko, an official with the mayor’s office, told the Associated Press (AP).

He said the building had a relatively modern basement bomb shelter designed to withstand air strikes.

Other officials had said earlier that some people had got out.

Ukraine’s ombudswoman, Ludmyla Denisova, said on the Telegram messaging app that the shelter had held up.

Satellite imagery on Monday from Maxar technology showed huge white letters on the pavement in front of and behind the theatre spelling out “Children” in Russian – “Deti” – to alert warplanes to those inside.

Russia’s military denied bombing the theatre or anywhere else in Mariupol on Wednesday.

The strike against the theatre was part of a furious bombardment of civilian sites in multiple cities over the past few days.

In the northern city of Chernihiv, at least 53 people had been brought to morgues over the past 24 hours, killed amid heavy Russian air attacks and ground fire, the local governor, Viacheslav Chaus, told Ukrainian TV on Thursday.

Ukraine’s emergency services said a mother, a father and three of their children, including three-year-old twins, were killed when a Chernihiv hostel was shelled.

Civilians were hiding in basements and shelters across the embattled city of 280,000,

“The city has never known such nightmarish, colossal losses and destruction,” Mr Chaus said.

At least 21 people were killed when Russian artillery destroyed a school and a community centre in Merefa, near the north-east city of Kharkiv, according to mayor Veniamin Sitov.

The region has seen heavy bombardment in a bid by stalled Russian forces to advance.

In eastern Ukraine, a municipal pool complex where pregnant women and women with children were taking shelter was also hit on Wednesday, according to Pavlo Kyrylenko, head of the Donetsk regional administration.

There was no word on casualties in that strike.

Ukrainian President Volodymyr Zelensky called for more help for his country in a video address to German legislators, saying thousands of people have been killed, including 108 children.

He also referred to the dire situation in Mariupol, saying: “Everything is a target for them.”

The address began with a delay because of a technical problem caused by an attack close to where Mr Zelensky was speaking, Bundestag deputy speaker Katrin Goering-Eckardt said.

Mr Zelensky’s office said Russia carried out further air strikes on Mariupol early on Thursday and attacks elsewhere around the country overnight, including in the Kalynivka and Brovary suburbs of the capital Kyiv.

There was no immediate word on casualties.

In Kyiv, where residents have been huddling in homes and shelters, emergency authorities said a fire broke out in an apartment building hit by remnants of a downed Russian rocket, killing one person.

Firefighters evacuated 30 people from the top floors of the 16-storey building and put out the blaze.

Russian artillery destroyed a school and a community centre in Merefa, near the north-east city of Kharkiv, according to Merefa mayor Veniamin Sitov.

There were no known civilian casualties.

The Kharkiv region has seen heavy bombardment as stalled Russian forces try to advance in the area.

The UN Security Council planned to meet on Thursday.

“Russia is committing war crimes and targeting civilians,” Britain’s UN delegation tweeted.

“Russia’s illegal war on Ukraine is a threat to us all.”

Russian President Vladimir Putin went on television on Wednesday to excoriate Russians who do not back him.

Russians “will always be able to distinguish true patriots from scum and traitors and will simply spit them out like a gnat that accidentally flew into their mouths”, he said.

“I am convinced that such a natural and necessary self-purification of society will only strengthen our country.”

He said the West is using a “fifth column” of traitorous Russians to create civil unrest.

“And there is only one goal, I have already spoken about it – the destruction of Russia,” he said.

The speech appeared to be a warning that his authoritarian rule, which had already grown tighter since the invasion began on February 24, shutting down Russian news outlets and arresting protesters, could grow even more repressive.

In a sign of that, Russian law enforcement announced the first known criminal cases under a new law that allows for 15-year prison terms for posting what is deemed to be “false information” about the Ukraine war.

Among those charged was Veronika Belotserkovskaya, a Russian-language cookbook author and blogger living abroad.

Both Ukraine and Russia this week have reported some progress in negotiations.

Kremlin spokesman Dmitry Peskov said talks should continue on Thursday in some form.

Some negotiators were breaking into working groups, “but there should be contacts today”, he said during his daily conference call with reporters.

He also said Moscow “can’t take into account” an International Court of Justice ruling ordering Russia to halt its operation in Ukraine, noting that both sides need to agree on implementing the ruling, and on Russia’s side “there can be no consent”.

Talks held by video on Wednesday appeared to wade deeply into technicalities.

Zelensky adviser Mikhailo Podolyak said Ukraine demanded a ceasefire, the withdrawal of Russian troops and security guarantees for Ukraine from several countries.

An official in Mr Zelenskyy’s office told the Associated Press that the main subject under discussion was whether Russian troops would remain in separatist regions in eastern Ukraine after the war and where the borders would be.

The official said Ukraine was insisting on the inclusion of one or more Western nuclear powers in the negotiations and on a legally binding document with security guarantees for Ukraine.

In exchange, the official said, Ukraine was ready to discuss a neutral military status.

Russia has demanded that Nato pledge never to admit Ukraine to the alliance or station forces there.

The fighting has led to more than three million people fleeing Ukraine, the UN estimates.

The death toll remains unknown, though Ukraine has said thousands of civilians have died.