More than 12.7 million people have been displaced since Russia invaded Ukraine two months ago.
Of these, 7.7 million sought safer shelter within Ukraine, and more than 5 million Ukrainians fled abroad, the UN refugee agency reports.
A spokesman said at a press briefing on Tuesday that 8.3 million people are expected to flee the country. The UN previously assumed 4 million Ukrainians would leave their country.
The organization says it needs more than 1.7 billion euros for aid to refugees in neighbouring countries of Ukraine.