Ukraine said Monday its forces had been pushed back from the centre of key industrial city Severodonetsk, where President Volodymyr Zelensky described a fight for "literally every meter."The cities of Severodonetsk and Lysychansk, which are separated by a river, have been targeted for weeks as the last areas still under Ukrainian control in the eastern Lugansk region.Regional governor Sergiy Gaiday said Monday Russian forces were "gathering more and more equipment" to "encircle" Severodonetsk.Moscow's troops had "pushed our units from the centre and continue to destroy our city," he said.The local Azot chemical plant, where hundreds of civilians have reportedly taken refuge, was being "heavily shelled," Gaiday added.Severodonetsk has been "de facto" blocked off after Russian forces blew up the "last" bridge connecting it to Lysychansk on Sunday, Eduard Basurin, a representative for pro-Russian separatists, said Monday.Ukrainian forces in the area have two choices, he said, "to surrender or die."Moscow-backed forces were also carrying out an offensive on the key city of Slovyansk, from "west, north and east," Basurin said.The capture of Severodonetsk would open the road for Moscow to Slovyansk and another major city, Kramatorsk, in their push to conquer the whole of Donbas, a mainly Russian-speaking region partly held by pro-Kremlin separatists since 2014.Weapons pleaUkrainian forces were fighting for "every town and village where the occupiers came", Zelensky said Monday in a message to mark the eighth anniversary of the liberation of Mariupol in the 2014 conflict.The port city in southern Ukraine was captured by Russian troops in May after a weeks-long siege."We are once again fighting for it and all of Ukraine," Zelensky said.Presidential advisor Mikhaylo Podolyak said Monday that Kyiv needed more arms deliveries to stop the conflict. "Being straightforward — to end the war we need heavy weapons," he said on Twitter.He listed items he said the Ukrainian army required, including hundreds of howitzers, tanks and armored vehicles.Currently, Russia's massed artillery in the area of Severodonetsk gave it a tenfold advantage, the commander-in-chief of the Ukrainian military, Valeriy Zaluzhny, said Sunday.  "Every metre of Ukrainian land there is covered in blood — but not only ours, but also the occupier's."In Lysychansk, Russian bombardments killed three civilians, including a six-year-old boy, Lugansk governor Gaiday said Monday.While in the city of Donetsk, separatist authorities said three people were killed and four wounded in Ukrainian shelling on a market in the Budonivskyi district of the city.'War crimes'On Monday, Amnesty International accused Russia of war crimes in Ukraine, saying that attacks on the north-eastern city of Kharkiv — many using banned cluster bombs — had killed hundreds of civilians. "The repeated bombardments of residential neighborhoods in Kharkiv are indiscriminate attacks which killed and injured hundreds of civilians, and as such constitute war crimes," the rights group said in a report on Ukraine's second-biggest city.Away from the battlefield, World Trade Organization members gathered in Geneva Sunday, with the threat posed to global food security by Russia's war top of the agenda.Tensions ran high during a closed-door session, where several delegates took the floor to condemn Russia's aggression, WTO spokesman Dan Pruzin told journalists.Just before Russia's deputy economic development minister Vladimir Ilichev spoke, around three dozen delegates "walked out," the spokesman said.On a farm near the city of Mykolaiv in the south, the harvest has been delayed by the need to undo the damage done by Russian troops that passed through the area in March."We planted really late because we needed to clear everything beforehand," including bombshells, Nadiia Ivanova, 42, told AFP.The farm's warehouses currently hold 2,000 tonnes of last season's grain but there are no takers.The railways have been partially destroyed by the Russian army, while any ship that sails faces the threat of being sunk.