Map: Where Ukraine refugees are heading
At least 1,189 civilians have been killed in Ukraine, according to the UN.
At least 4,019,287 people have fled Ukraine to neighboring countries since Russian forces invaded the eastern European country on Feb. 24, according to the United Nations refugee agency, UNHCR.
The majority of refugees have escaped to Poland, Romania, Moldova, Hungary and Slovakia.
The U.N. reports 3,090 civilian casualties in Ukraine, including 1,189 deaths and 1,901 injuries as of March 28. However, the organization says the real toll is much higher.
At least 202,000 of the refugees are third-country nationals, according to the International Organization for Migration (IOM).
Shortly after the crisis began, UNHCR staff reported lines that were miles long at the Polish border. In Romania, people were waiting up to 20 hours to enter, according to agency staff.
The 37-mile trek from the Ukrainian city of Odessa to the border of Moldova took some refugees 24 hours to make, the agency said.
In Hungary, arrivals were “steady and waiting times vary.”
Ukrainian citizens have also been displaced within the country, according to Filippo Grandi, the UNHCR commissioner, but it remains unknown how many. He also said there is a “growing number of unaccompanied and separated children."
In what Russian President Vladimir Putin has called a "special military operation," Russian forces continue to try and push through Ukraine, as Ukrainian forces hold steady in the fight.
Many reasons have been cited as Putin's reasoning for the attacks, including the threat of Ukraine's membership in NATO, the Western military alliance. But Putin has also tried to question Ukraine's legitimacy as a country and claimed that the country needed to be liberated from Nazis.
Ukrainian President Volodymyr Zelenskyy has vowed to remain in Kyiv and fight against Russian forces.
"We are all here. Our military are here, as are our people and whole society," Zelenskyy said in a video posted to Facebook. "We're all here defending our independence and our country. And we'll go on doing that. Glory to our defenders! Glory to Ukraine."