The United Nations has launched an emergency appeal for $1.7 billion in humanitarian aid for those affected by Russia's invasion of Ukraine.
"This is the darkest hour for the people of Ukraine," UN humanitarian chief Martin Griffiths said in a statement on March 1.
"We need to ramp up our response now to protect the lives and dignity of ordinary Ukrainians. We must respond with compassion and solidarity."
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The UN's refugee agency, the UNHCR, says that more than 660,000 refugees have fled Ukraine since Russia launched its unprovoked attack on February 24, while around one million more are estimated to have been internally displaced as fighting rages in many areas across the country.
Moreover, the UN said it estimates that 12 million people inside Ukraine will need relief and protection, while more than 4 million Ukrainian refugees may need protection and assistance in neighboring countries in the coming months.
"We are looking at what could become Europe's largest refugee crisis this century," said UNHCR chief Filippo Grandi.
"While we have seen tremendous solidarity and hospitality from neighboring countries in receiving refugees, including from local communities and private citizens, much more support will be needed to assist and protect new arrivals."
Under the appeal, the UNHCR is seeking $1.1 billion to assist 6 million people inside Ukraine for an initial three months.
An interagency refugee response plan calls for at least $550.6 million to help refugees in Poland, Moldova, Hungary, Romania, Slovakia, and other countries in the region that are taking in thousands of refugees from Ukraine each day.