Ukraine said on 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 metre".
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 on Monday Russian forces were "gathering more and more equipment" to "encircle" Severodonetsk, and that they had "pushed our troops from the centre and continue to destroy our city".
The local Azot chemical plant, where hundreds of civilians have reportedly taken refuge, was being "heavily shelled", Mr. Gaiday said.
In Lysychansk, bombardments killed three civilians, including a six-year-old boy, he said.
Severodonetsk had been "de facto" blocked off after Russian forces blew up the "last" bridge connecting it to Lysychansk Sunday, Eduard Basurin, a representative for pro-Russian separatists, said on Monday.
"The Ukrainian units that are there, they are there forever. They have two options: to surrender or die," Mr. Basurin said.
On Sunday, Mr. Zelensky said the latest fighting in Severodonetsk was "very fierce", adding that Russia was deploying undertrained troops and using its young men as "cannon fodder".
Russia's amassed artillery in that region gave it a tenfold advantage, the commander-in-chief of the Ukrainian military, Valeriy Zaluzhny, said on Sunday.
"Every metre of Ukrainian land there is covered in blood — but not only ours, but also the occupier's."
The capture of Severodonetsk would open the road for Moscow to another major city, Kramatorsk, in their steps toward conquering the whole of Donbas, a mainly Russian-speaking region partly held by pro-Russian separatists since 2014.
On Monday, Amnesty International accused Russia of war crimes in Ukraine, saying that attacks on the northeastern city of Kharkiv — many using banned cluster bombs — had killed hundreds of civilians.
"The repeated bombardments of residential neighbourhoods 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 on Sunday, with the threat posed to global food security by Russia's war in wheat-producing Ukraine top of the agenda.
Tensions ran high during a closed-door session, where several delegates took the floor to condemn Russia's war, including Kyiv's envoy who was met with a standing ovation, WTO spokesman Dan Pruzin told journalists.
Just before Russian Minister of Economic Development Maxim Reshetnikov 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, said.
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.
The war has prompted Finland and Sweden to give up decades of military non-alignment and seek to join the NATO alliance.
But Turkey is blocking their bids and NATO chief Jens Stoltenberg said on Sunday the issue may not be resolved in time for an alliance summit later this month.
Speaking to AFP, Mikhail Kasyanov, Russia's Prime Minister from 2000 to 2004, said he thought President Vladimir Putin was "out of it", after seeing the Russian leader summon the country's top brass for a theatrical meeting three days before the invasion on February 24.
"I knew a different Putin," said Mr. Kasyanov, 64, who served under Mr. Putin but has become one of the Kremlin's most vocal critics.
Mr. Kasyanov predicted the war could last for up to two years and said it is imperative that Ukraine win.
"If Ukraine falls, the Baltic states will be next," he said.
The United States and Europe have sent weapons and cash to help Ukraine blunt Russia's advance, alongside punishing Moscow with unprecedented economic sanctions.
Russian forces said on Sunday they had struck a site in the town of Chortkiv in western Ukraine storing U.S.- and EU-supplied weapons.
Russia's Defence Ministry said the strike destroyed a "large depot of anti-tank missile systems, portable air defence systems and shells provided to the Kyiv regime by the U.S. and European countries".
The strike — a rare attack by Russia in the relatively calm west of Ukraine — left 22 people injured, regional governor Volodymyr Trush said.
Concerns eased on Sunday over Ukraine's largest nuclear power plant in Zaporizhzhia. Captured months ago by Russian forces but still operated by Ukrainians, the station had ceased transmitting vital safeguards data two weeks ago.
But plant officials working with the International Atomic Energy Agency have succeeded in restoring transmission, the IAEA said.
Rafael Grossi, director general of the UN agency, said it still wanted to send inspectors to the plant "as soon as possible".
