As its chief arrives in Lviv, refugee agency says 'senseless war' has driven 4,019,287 to flee Ukraine; another 6.5 million displaced within the country

Refugee agency praises neighboring countries' compassion for 'extreme plight' of refugees; most of those who crossed borders to escape entered Poland

Refugee commissioner estimates over a quarter of a million have escaped to Poland, 84,500 are in Hungary, 36,400 in Moldova, over 32,500 in Romania and about 30,000 in Slovakia

Move comes amid concerns of instability and upended humanitarian efforts after Taliban takeover, compounded by an ongoing drought

Figures climbed by 3 million during 2020, to a record-breaking 82 million total; UNHCR chief says factors that caused people to flee continued during pandemic