Vladimir Putin’s renewed assault on the Donbas region of eastern Ukraine could last for “several months”, a senior national security official told the government as Boris Johnson pledged more artillery weapons to Kyiv.
The prime minister told his cabinet at Downing Street that Ukraine’s position was “perilous” as the Russian president was thought to want to be able to declare a victory of some sort “regardless of the human cost”.
“This will become an artillery conflict; they need support with more artillery, that is what we will be giving them ... in addition to many other forms of support,” Johnson told ministers.
Russia attacked along a 300-mile front in eastern Ukraine on Tuesday as part of a full-scale ground offensive to take control of the country’s eastern industrial heartland in what Ukrainian officials called a “new phase of the war”.
The stepped-up assaults are focused on the Donbas regions of Donetsk and Luhansk, with the Russian forces trying to advance in several sections, including from neighbouring Kharkiv.
Some 12 million Ukrainians have already been displaced by fighting, including 4.9 million who have fled to neighbouring countries and 7.1 million internally.
The UN estimates that over a million more people will be displaced into neighbouring countries as the Ukraine government urges residents to leave the east amid Russia’s latest assault on the region.
Mr Johnson was due to take part in an international conference call on Tuesday with US president Joe Biden and leaders of France, Germany, Italy, Japan, Canada, Poland, Romania and the EU to discuss further assistance to the Kyiv administration on its 55th day of resistance to the Russian invasion.
Ukraine said the new Russian assault had resulted in the capture of Kreminna, an administrative centre of 18,000 people in Luhansk, one of the two Donbas provinces.
Russian forces were attacking "on all sides", authorities were trying to evacuate civilians and it was impossible to tally the civilian dead, Luhansk regional governor Serhiy Gaidai said.
President Volodymyr Zelensky told Ukrainians in a video address overnight that they would withstand the new advance.
"No matter how many Russian troops they send there, we will fight. We will defend ourselves," he said.
In Moscow, Russian foreign minister Sergei Lavrov confirmed that "another stage of this operation is beginning".
Driven back by Ukrainian forces in March from an assault on Kyiv in the north, Russia has instead poured troops into the east for the Donbas offensive. It has also made long-distance strikes at other targets including the capital.
In Mariupol, the scene of the war's heaviest fighting and worst humanitarian catastrophe, a last group of Ukrainian defenders defied Russian calls to surrender.
"All who lay down their arms are guaranteed to remain alive," the Russian defence ministry said.
Mariupol has been besieged since the war's early days. Tens of thousands of residents have been trapped with no access to food or water and bodies litter the streets. Ukraine believes more than 20,000 civilians have died there.
Capturing it would link pro-Russian separatist territory with the Crimea region that Moscow annexed in 2014.
In Kharkiv, Ukraine's second city, shells hit the southeastern Nemyshlianskyi district in the afternoon, wrecking one apartment building and damaging others.
Three bodies of people apparently killed by shrapnel lay on the pavement.
"They are sabotaging the whole city," said 79-year-old Fyodor Bondarenko, watching as one body was carried into an ambulance while the crump of shelling sounded in the background.
Reuters contributed to this report.
