Some 3 million people have fled Ukraine since Russian forces invaded almost three weeks ago, the UN's International Organization for Migration (IOM) said on March 15.
Russia denies targeting civilians, alleging its actions are a "special military operation" to demilitarize and "denazify" Ukraine.
Ukraine and Western allies have called this a baseless pretext for Moscow's invasion of a democratic country.
More than 150,000 third-country nationals are among the refugees, IOM spokesperson Safa Msehli wrote on Twitter.
According to government data collated by the UN Refugee Agency (UNHCR), most Ukrainian refugees fleeing their country have arrived in Poland.
The Polish border force reported on March 15 that 1.83 million Ukrainian refugees had arrived since the war began.
Some 453,432 have been counted in Romania, 337,215 in Moldova, 263,888 in Hungary, and 213,000 in Slovakia, according to the UNHCR website.
Some 142,994 refugees had fled to Russia, UNHCR said, citing the latest data from Moscow, while a relatively small number have fled to Belarus.
A significant number of refugees are starting to move further west, with 300,000 individuals to date having gone to Western Europe, the UNHCR said.
Nearly 3 Million Have Fled Fighting In Ukraine, UN Says
Refugees from Ukraine arrive at the train station in Przemysl, eastern Poland, earlier this month.