ZURICH (Reuters) - A million people have fled Ukraine in a week after Russia invaded the country, the head of the United Nations refugee agency said on Twitter.

       "In just seven days we have witnessed the exodus of one million refugees from Ukraine to neighbouring countries," UNHCR head Filippo Grandi posted.

       "For many millions more, inside Ukraine, it's time for guns to fall silent, so that life-saving humanitarian assistance can be provided."

       (Reporting by Michael Shields; Editing by Jacqueline Wong)