The word “children” was written in huge letters on the ground outside the two ends of the theater, so that it could be seen from the planes above. Russia has denied the allegations in a statement issued Friday stating “Similar, baseless allegations concerning Russia’s intelligence have been made more than once. The Drama Theater in Mariupol, Ukraine, which was used as a bomb shelter by civilians when it was hit during the bombing of the port city by Russia, is shown in a photo provided by the Ministry of Internal Affairs of Ukraine, March 18, 2022. MINISTRY OF INTERIOR / Anadolu Agency / Getty The United Nations said on Friday it was receiving more and more information about mass graves in Mariupol, including one that appeared to hold about 200 victims of the war. Ukrainian officials estimate that there are still about 100,000 civilians trapped in the city, where the Russian siege cut off food, water, gas and electricity supplies weeks ago. Some 10 million Ukrainians have been forced to flee their homes after just one month of war, with at least 3.5 million being driven to seek refuge in neighboring countries. More than half of them have crossed Ukraine’s western border with Poland, where President Joe Biden visited on Friday in solidarity with both refugees and aid workers. “With each day of our defense, we are getting closer to the peace we so desperately need,” Ukrainian President Volodymyr Zelensky said in a speech on Thursday afternoon. “We can not stop for a minute, because every minute determines our fate, our future, whether we will live.” Ukraine holds ground one month after the Russian invasion 02:46 CBS News senior foreign correspondent Holly Williams visited a Ukrainian military base and saw some of these defenses – and a group of young Ukrainian recruits preparing to join the fight. Lieutenant Miroslav Hai was a filmmaker and a reserve soldier before Russia invaded his country and said Ukrainians would continue to defend their nation and their freedom no matter what, even if Putin used nuclear weapons. “The normal man does not want war. But he must,” he said. “Because if we do not stop [Russia] now, our children will start a war with Russia… If we do not stop Putin in Ukraine, more will go. “If we do not stop Putin in Ukraine, he will go to other countries.” Officials told CBS News that the recruits at the base receive basic training just one week before being sent to the front line. At the arsenal, Williams was told that they were receiving weapons from NATO countries, but that they needed more, as well as vehicles to move troops. Hai said he hated thinking about what Russia was doing to Ukraine. “I think we have a somewhat similar situation with the Soviet Union and Afghanistan,” he told CBS News. “Afghanistan destroyed the Soviet Union and I hope Ukraine will destroy the Russian Empire.” Biden promotes European unity at historic NATO summit 03:54 On Friday, the Russian Defense Ministry said that 1,351 of its soldiers had been killed in Ukraine since the start of the “special military operation”. The ministry said another 3,825 troops had been wounded, although NATO believed that number was much higher, estimating that between 7,000 and 15,000 Russian soldiers had been killed in the war so far. Earlier this month, Ukrainian President Volodymyr Zelenskyy said 1,300 Ukrainian soldiers had been killed defending the country from Russian invasion. Analysts told the Washington Post that the actual number of Ukrainian casualties could also be higher. In some key areas around the capital, Ukrainian forces managed to repel Russian troops. A Russian supply ship was wrecked on Thursday in a port not far from Mariupol as Ukrainians pushed for the recapture of a city near Kyiv claimed by Russian invaders. But while Putin’s ground forces have been largely swamped for weeks, especially around Kyiv, they have continued to push against Ukraine’s defenders in the south and east. On Friday, officials said the northern city of Chernihiv – decimated after weeks of incessant bombing but still under Ukrainian control – had been completely cut off by Russian forces. “The city has been conditionally surrounded, operationally by the enemy,” the regional governor said on television, adding that Chernihiv was still under fire from warplanes and artillery. More