Nearly 35,000 more Ukrainians fled west in 24 hours to escape the Russian war in their country, the United Nations said Wednesday. UNHCR, the UN refugee agency, said 4,278,789 Ukrainians had fled across the borders since the war began on February 24 -- a figure up 34,194 since Tuesday.

The UN's International Organization for Migration estimates that 7.1 million internally displaced people had fled their homes but were still in Ukraine.

The IOM says that in addition to Ukrainian refugees, more than 206,000 non-Ukrainians living, studying or working in the country have also left. 

This means that in total, more than a quarter of the population have been forced to flee their homes.

Before the Russian invasion, Ukraine had a population of 37 million in the regions under government control, excluding Russia-annexed Crimea and the pro-Russian separatist regions in the east.

Women and children account for 90 percent of those who have left Ukraine, with men aged 18 to 60 eligible for military call-up and unable to leave.

Linda Thomas-Greenfield, the US ambassador to the UN in New York, told the UN Security Council: "Ukraine's neighbours are bearing the brunt of Europe's most significant refugee crisis since World War II."

Here is a breakdown of how many Ukrainian refugees have fled to neighbouring countries, according to UNHCR:

- Poland -

Nearly six out of 10 Ukrainian refugees -- 2,490,447 so far -- have crossed into Poland, according to the UN. Polish border guards said the number had reached 2.5 million on Tuesday.

Many people who go to Ukraine's immediate western neighbours travel on to other states in Europe's Schengen open-borders zone. UNHCR said Wednesday that around 83,000 refugees have now crossed into Italy.

Polish border guards say that since the war began, 471,000 people have left Poland for Ukraine.

Before the crisis, Poland was already home to around 1.5 million Ukrainians, chiefly migrant workers.

- Romania -

A total of 654,825 Ukrainians entered the EU member state, including a large number who crossed over from Moldova, wedged between Romania and Ukraine. 

The vast majority are thought to have gone on to other countries. 

Thomas-Greenfield, who recently returned from Moldova and Romania, told the Security Council: "I saw with my own eyes the refugee crisis caused by Russia's unconscionable war. I spoke to refugees who indicated to me their desires to return to their home. 

"Behind those destroyed buildings are destroyed lives and destroyed families. I met with women and children who had fled Ukraine, who stuffed their lives into backpacks and left the only home they had ever known."

- Moldova -

The Moldovan border is the closest to the major port city of Odessa. Some 399,039 Ukrainians have crossed into the non-EU state, one of the poorest in Europe.

Most of those who have entered the former Soviet republic of 2.6 million people have moved on.

- Hungary -

A total of 394,728 Ukrainians have entered Hungary. 

- Russia -

Another 398,932 refugees had sought shelter in Russia as of March 29.

In addition, 113,000 people crossed into Russia from the separatist-held pro-Russian regions of Donetsk and Lugansk in eastern Ukraine between February 21 and 23. 

- Slovakia -

A total of 302,417 people crossed Ukraine's shortest border into Slovakia.

- Belarus -

Another 17,317 refugees had made it north to Russia's close ally Belarus.