About 300 people died in a Russian air strike last week on a theatre being used as a bomb shelter in the besieged Ukrainian city of Mariupol, the city’s government has said.

When the theatre was struck on March 16, an enormous inscription reading “Children” was posted outside in Russian, intended to be visible from the skies above.

It was not clear whether emergency workers have finished excavating the site.

Soon after the air strike, Ludmyla Denisova, the Ukrainian Parliament’s human rights commissioner, said more than 1,300 people had been sheltering in the building.

Mariupol has suffered some of the worst devastation of the war, which has seen Russia relentlessly besiege and attack Ukraine’s cities.

The misery inside them is such that nearly anyone who can is trying to leave and those left behind face desperate food shortages in a country once known as the breadbasket for the world.

Unable to sweep with lightning speed into Kyiv, their apparent aim on February 24 when the Kremlin launched the war, Russian forces are instead raining down shells and missiles on cities from afar.

The outskirts of Kharkiv were shrouded by foggy smoke on Friday, with shelling constant since early in the morning.

In a city hospital, several wounded soldiers arrived, with bullet and shrapnel wounds, a day after doctors treated a dozen civilians. Even as doctors stabilised the direst case, the sound of shelling could be heard in the surgery ward.

Russia’s military claimed on Friday that it destroyed a massive Ukrainian fuel base used to supply the Kyiv region’s defences, with ships firing a salvo of cruise missiles, according to the Interfax news agency. Videos on social media showed an enormous fireball explosion near the capital.

Kyiv, like other cities, has seen its population dramatically reduced in the vast refugee crisis that has seen more than 10 million displaced and at least 3.5 million fleeing the country entirely.

In the capital, over 260 civilians have died and more than 80 buildings been destroyed since the start of the war.

Ukrainian President Volodymyr Zelenskyy urged his country to keep up its military defence and not stop “even for a minute”. He used his nightly video address on Thursday to rally Ukrainians to “move toward peace, move forward”.

“With every day of our defence, we are getting closer to the peace that we need so much. We can’t stop even for a minute, for every minute determines our fate, our future, whether we will live.”

He said thousands of people, including 128 children, died in the first month of the war. Across the country, 230 schools and 155 kindergartens have been destroyed. Cities and villages “lie in ashes”, he said.

At an emergency Nato summit in Brussels on Thursday, Mr Zelensky pleaded with the Western allies via video link for planes, tanks, rockets, air defence systems and other weapons, saying his country is “defending our common values”.

In a video address to EU leaders, meanwhile, Mr Zelensky thanked them for working together to support Ukraine and impose sanctions on Russia, including Germany’s decision to block Russia from delivering natural gas to Europe through the new Nord Stream 2 pipeline.

But he lamented that these steps were not taken earlier, saying there was a chance Russia would have thought twice about invading.

While millions of Ukrainians have fled west, Ukraine accused Moscow of forcibly removing hundreds of thousands of civilians from shattered cities to Russia to pressure Kyiv to give up.

Lyudmyla Denisova, Ukraine’s ombudsperson, said 402,000 people, including 84,000 children, had been taken against their will into Russia, where some may be used as “hostages” to pressure Kyiv to surrender.

The Kremlin gave nearly identical numbers for those who have been relocated, but said they were from predominantly Russian-speaking regions of Donetsk and Luhansk in eastern Ukraine and wanted to go to Russia.

Pro-Moscow separatists have been fighting for control for nearly eight years in those regions, where many people have supported close ties to Russia.