Russia begins large-scale military action to seize eastern Ukraine

Ukrainian government officials warned Russian war-planes were preparing to drop five-tonne bombs on the Azovstal plant in the besieged city of Mariupol. Ukrainian soldiers have been holding out in tunnels under the factory for seven weeks.

The underground complex is also being used as a shelter by hundreds of civilians including children. They were about to be wiped out, the officials said.

Earlier on Monday four Russian rockets smashed into the western city of Lviv, killing seven people and injuring at least 11. Three hit military infrastructure. But the fourth appeared to have missed its target and landed in a car repair workshop.

It said it had hit areas across the country, including the cities of Kharkiv and Zaporizhzhia, as well as the Donetsk and Dnipropetrovsk regions and the southern port of Mykolaiv.

A powerful explosion was reported to have rocked Vasylkiv, a town south of Kyiv that is home to a military airbase, according to residents. There was also further deadly shelling in Kharkiv. Over the past four days, 18 people have been killed and 106 injured.

That could translate to about 50,000 to 60,000 troops, based on what the Pentagon said at the start of the war was the typical unit strength of 700 to 800 soldiers, but the numbers are difficult to pinpoint at this stage in the fighting.

The official also said that four US cargo flights arrived in Europe on Sunday with an initial delivery of weapons and other materials for Ukraine as part of a $800m (£615m) package announced by Washington last week. And training of Ukrainian personnel on US 155mm howitzers is set to begin in the next several days.

The capture of Mariupol, where Ukraine estimates 21,000 people have been killed, is seen as key, and not just because it would deprive Ukraine of a vital port and complete a land bridge between Russia and the Crimean Peninsula, seized by Moscow eight years ago.

The US defence official said that if Russian forces succeed in taking full control of Mariupol, that could free up nearly a dozen battalion tactical groups for use elsewhere in the Donbas.