Zelenskyy Ready for Negotiations With PutinWASHINGTON — Ukrainian President Volodymyr Zelenskyy said he is ready for negotiations with Russian President Vladimir Putin but warned that failure to reach an agreement "would mean that this is a third World War." “I think that without negotiations, we cannot end this war,” he told CNN’s Fareed Zakaria in an interview broadcast Sunday. Zelenskyy has called for comprehensive peace talks with Moscow that restore the territorial integrity and provide justice for Ukraine. Russia's lead negotiator has said in recent days the sides have moved closer to agreement on the issue of Ukraine dropping its bid to join NATO and adopting neutral status. Zelenskyy told CNN that Russian forces entered Ukraine “to exterminate us, to kill us,” but he vowed that Ukraine would not concede its sovereignty or its integrity. “Russians have killed our children. You cannot reverse the situation anymore. You cannot demand from Ukraine to recognize some territories as independent republics. These compromises are simply wrong,” Zelenskyy said. Mariupol In the besieged city of Mariupol, an art school where about 400 people had found shelter was bombed by Russian forces. Mariupol’s city council said Sunday that the building was destroyed in the attack. Information about survivors was not immediately available. U.S. Defense Secretary Lloyd Austin told CBS’s “Face the Nation” that he thinks Russian forces are resorting to these brutal civilian attacks because its military “campaign is stalled.” “This is really disgusting,” Austin said. Just a few days earlier a Russian airstrike targeted a theater where hundreds of people had been sheltering. The word “CHILDREN” had been written in Russian in big letters visible from the sky on the ground just outside the theater, to alert Russian forces of who was inside. More than 100 have been rescued from the theater, and it is still unclear how many casualties and fatalities the attack caused. The city continues to resist Russian military forces, who are having to engage in attrition tactics and urban fighting that requires going from building to building. "Mariupol has not yet fallen. It is out of food, fuel, water, everything except for heart. They are still fighting very hard,” retired Gen. David Petraeus told CNN Sunday. Thousands of residents of Mariupol have been forcibly taken from their homes to Russian territory, according to a Mariupol city council statement on its Telegram channel. "The occupiers illegally took people from the Livoberezhny district and from the shelter in the sports club building, where more than a thousand people (mostly women and children) were hiding from the constant bombing," the statement said. "What the occupiers are doing today is familiar to the older generation, who saw the horrific events of World War II, when the Nazis forcibly captured people," Mariupol Mayor Vadym Boichenko said. Russia still stalled Austin said that Russian forces across the country have been ineffective as Ukrainian forces continue to attrit Russian troops with weapons provided by the U.S. and NATO allies. “It’s had the effect of him (Putin) moving his forces into a woodchipper,” Austin told CBS. U.S. officials have estimated that Ukrainians have killed more than 3,000 Russian troops since the invasion began. At least five of those have been senior Russian officers, according to the Ukrainian government. Petraeus said Sunday at least four of the five Russian generals’ deaths “are absolutely confirmed,” adding that Ukrainian snipers “have just been picking them off left and right.” Russian troops have failed to seize control of the Ukrainian capital, Kyiv, a major objective of the Kremlin, even as the invasion enters its fourth week. Ukraine’s National Police said in a statement Saturday on Telegram that Russia was attacking the northwestern suburbs of Kyiv, while the regional Kyiv government reported the city of Slavutych, north of Kyiv was “completely isolated.” Mykolaiv Meanwhile, officials in Ukraine have yet to release the death toll following a Russian missile attack Friday on a military base where soldiers were sleeping in barracks, now destroyed, in the southern Ukrainian city of Mykolaiv. One soldier told AFP that 50 bodies have been found, while another said there could be as many as 100 dead under the rubble. Mykolaiv is located 130 kilometers from the strategic military port of Odesa. Russia said Saturday that its hypersonic missiles had destroyed an underground depot for missiles and ammunition Friday in Ukraine’s western Ivano-Frankivsk region. Russian news agencies said it was the first time it used the advanced weapons system in Ukraine since it invaded February 24. U.S Defense Secretary Austin said Sunday he could not confirm or dispute whether Russia had used those types of weapons in Ukraine but added he would not see it as a gamechanger if they had. A Ukrainian air force representative verified the attack in the Ivano-Frankivsk region, but said Ukraine had no information on the type of missiles used. In other developments, humanitarian corridors were opened Saturday, allowing a total of 6,623 people to evacuate from various Ukrainian cities, according to Kyrylo Tymoshenko, deputy head of the president's office. He reported online that 4,128 of those people escaped from Mariupol. There are plans to open more corridors Sunday. The United Nations human rights office (OHCHR) reports that at least 902 civilians have been killed and upward of 1,459 have been wounded as of Saturday, while warning the actual count likely is higher. Most of the deaths were from explosions caused by shelling from heavy artillery and multiple missiles and air strikes, OHCHR said. The Ukrainian prosecutor general’s office said 112 of those killed were children. Millions of people have fled their homes since the Russian invasion. “The war in Ukraine is so devastating that 10 million have fled — either displaced inside the country, or as refugees abroad,” U.N. High Commissioner for Refugees Filippo Grande tweeted Sunday. U.N. correspondent Margaret Besheer contributed to this report. Some information also came from The Associated Press, Agence France-Presse and Reuters.