KYIV/LVIV, Ukraine, March 16 (Reuters) - U.S. President Joe Biden on Wednesday called Russian leader Vladimir Putin a war criminal in comments the Kremlin said were "unforgivable" as it insisted the war in Ukraine was "going to plan" amid talk of compromise at peace talks.Kremlin forces kept up their bombardments of besieged cities, including intensified shelling of the capital Kyiv, and civilians waiting in line for bread and sheltering in a theatre were killed, according to U.S. and Ukrainian officialsMoscow has yet to capture any of Ukraine's biggest cities following its invasion that began on Feb. 24, the largest assault on a European state since World War Two, raising fears of wider conflict in the West.Putin on Wednesday said he would discuss neutral status for Ukraine and that what he calls a "special military operation" to demilitarize the country was "going to plan". Kyiv and allies say his actions are an unprovoked incursion, and more than 3 million Ukrainians have fled and hundreds have died.The United States announced an additional $800 million in security assistance to Ukraine to fight Russia, with the new package including drones, anti-armour and anti-aircraft systems."More will be coming as we source additional stocks of equipment that ... we are ready to transfer," Biden said, later condemning Putin."He is a war criminal," he told reporters.Kremlin spokesman Dmitry Peskov said the comment was "unacceptable and unforgivable rhetoric", according to Tass news agency.Ukraine still hopes for a diplomatic solution. President Volodymyr Zelenskiy said negotiations were becoming "more realistic" and Russia said proposals under discussion were "close to an agreement."The U.S. Embassy in Kyiv said Russian forces had shot dead 10 people waiting in line for bread in Chernihiv, northeast of Kyiv. Russia denied the attack and said the incident was a hoax.Emergency services said rescue workers had found the bodies of five people during searches of shell-hit buildings.In the besieged southern port of Mariupol, the city council said Russian forces bombed a theatre where civilians were sheltering. The number of casualties was not known.Russia denied it had carried out an air strike against the theatre. Reuters could not independently verify the information.Maxar Technologies, a private U.S. company, distributed satellite imagery that it said was collected on March 14 and showed the word "children" in large Russian script painted on the ground outside the red-roofed Mariupol Drama Theatre.https://www.reuters.com/world