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The United Nations is basing its humanitarian aid plans on 4 million Ukrainian refugees seeking safety, but it may need to increase that number shortly, the head of the UN's Refugee Agency said on Tuesday.
Some 2 million Ukrainians, mostly women and children, have already left the country since Russia began its invasion on Feb.24, the UNHCR said. Russia calls its actions in Ukraine a "special operation".
But this may be just the start, said Filippo Grandi, the head of the agency.
"How many will come? This depends very much on how the war evolves. We have a planning figure of 4 million refugees in total," Grandi told Reuters during a visit to Oslo, stressing this was not an official forecast.
"These are planning figures on how many supplies you buy, how much money you put aside, so we can scale it up quite quickly. I think we may have to do it soon because we are already at 2 million (refugees)."
Much depended on how the war will evolve, he said.
"Will the war advance towards Western Ukraine quickly? Then we will have huge influxes because a lot of people have taken refuge in that region. Will Kyiv fall? That will also trigger a large movement (of people)," he said.
Earlier on Tuesday, Grandi said that, after the first wave of refugees from Ukraine, there is likely to be a second wave consisting of more vulnerable refugees, who may not have friends and family to rely on for help.
"If the war continues we will start seeing people that have no resources and no connections," Grandi told a news conference.
"That will be a more complex situation to manage for European countries going forward, and there will need to be even more solidarity by everybody in Europe and beyond," he said.
(Reporting by Gwladys Fouche and Victoria Klesty; Editing by Catherine Evans and Jonathan Oatis)