Air raid sirens rang out across much of the east of Ukraine on Saturday morning, officials said, as Luhansk Governor Serhiy Gaidai urged people in a televised address to leave as Russia was amassing forces for an offensive.
"They (Russia) are amassing forces for an offensive and we see the number of shelling has increased," Mr Gaidai told public television.
He said that some 30 per cent of residents still remain in cities and villages across the region and have been asked to evacuate.
Ukraine has increasingly been warning that Russia plans intensified attacks in the country's east and south after withdrawing its troops from areas to the north of the capital, Kyiv.
The United States said this week that Moscow probably plans to deploy tens of thousands of soldiers in eastern Ukraine.
Ukraine's Deputy Prime Minister Iryna Vereshchuk said that 10 humanitarian corridors have been agreed for the evacuation of people across the country
President Volodymyr Zelenskyy called for a "firm global response" to Friday's missile attack on a train station crowded with women, children and the elderly in Kramatorsk, in the Donetsk region. The city mayor, who estimated 4,000 people were gathered there at the time, said at least 52 died.
Russia's defence ministry denied responsibility for the attack, saying in a statement the missiles that struck the station were used only by Ukraine's military and that Russia's armed forces had no targets assigned in Kramatorsk on Friday.
All statements by the Ukrainian authorities on the attack were "provocations," it said.
War could last years
Russia's incursion, which has already lasted over six weeks, has forced more than 4 million people to flee abroad, killed or injured thousands, left a quarter of the population homeless, and turned cities into rubble.
The Kremlin said on Friday that what it calls a "special operation" to demilitarise and "denazify" Russia's southern neighbour could end in the foreseeable future with its aims being achieved through work by the Russian military and peace negotiators.
But NATO Secretary General Jens Stoltenberg, whose organisation like Ukraine has dismissed Russia's arguments as a pretext for an unprovoked invasion, warned the war could last months or even years.
The General Staff of Ukraine’s armed forces said Moscow was preparing for a thrust to try to gain full control of the eastern Donbas regions of Donetsk and Luhansk partly held by Moscow-backed separatists since 2014, after withdrawing forces from the Kyiv region.
The British Defence Ministry said in a briefing it expected air attacks to increase in the south and east as Russia seeks to establish a land bridge between Crimea - which Moscow annexed in 2014 - and the Donbas but Ukrainian forces were thwarting the advance.
Ten humanitarian corridors to evacuate people from besieged regions have been agreed for Saturday, including one for people evacuating by private transport from the devastated southeastern port city of Mariupol, Deputy Prime Minister Iryna Vereshchuk said.
Kramatorsk mayor Oleksander Honcharenko said he expected just 50,000-60,000 of his city's 220,000 population to remain within a week or two.
Cluster munitions
Regional governor Pavlo Kyrylenko said Kramatorsk station was hit on Friday by a Tochka U short-range ballistic missile containing cluster munitions, which explode in mid-air, spraying bomblets over a wider area.
Cluster munitions are banned under a 2008 convention. Russia has not signed it but has previously denied using such armaments in Ukraine.
Reuters was unable to verify the details of the attack.
In Washington, a senior defence official said the United States did not accept the Russian denial and believed Russian forces had fired a short-range ballistic missile in the train station attack.
The European Union and Britain joined in condemnation of the incident which took place on the same day European Commission President Ursula von der Leyen visited Kyiv to show solidarity and accelerate Ukraine's membership process.
International revulsion
Friday's attack added to a wave of international revulsion at the high level of civilian casualties following the discovery of hundreds of dead bodies in the town of Bucha near Kyiv after Russian soldiers withdrew.
Russia has called allegations that its forces executed civilians there a "monstrous forgery".
Visiting the town on Friday as a forensics team began exhuming a mass grave in Bucha, Ms von der Leyen said it had witnessed the "unthinkable".
She later handed Mr Zelenskyy a questionnaire forming a starting point for the EU to decide on membership.
The bloc also overcame some divisions to adopt new sanctions, including bans on the import of coal, wood, chemicals and other products alongside the freezing of EU assets belonging to Mr Putin's daughters and more oligarchs.
Mr Zelenskyy said in a video address the West must do more, including an energy embargo and cutting off all Russian banks from the global financial system.
