A week after launching its invasion of Ukraine, Russia said its forces took control of the first sizable city on Wednesday, seizing Kherson, in the south, as fighting raged around the country and Western nations tightened an economic noose around Russia.

More than half a million Ukrainians have fled the fighting since Russian President Vladimir Putin ordered a full-scale invasion of his southern neighbour nearly a week ago.

Russian bombardments of Ukrainian cities continued, with a...