The pounding of the besieged southern port city of Mariupol intensified Sunday as Russia's bloody assault on Ukraine waded deeper into its fourth week. An estimated 3 million refugees have fled Ukraine since Russia's Feb. 24 invasion. Most fled to Poland, and an estimated 350,000 have entered Moldova, one of Europe's poorest countries. Most are women and children, as most men of fighting age have been ordered to stay behind to defend their country. Meanwhile, fears arose over the prospect of Russian-organized "concentration and prisoner camps" after the Mariupol city council said Ukrainian passports were taken from people who were given a piece of paper that "has no legal weight and is not recognized throughout the civilized world." The city council also claimed Russian soldiers have forced more than a thousand city residents to be relocated to Russia. The U.S. ambassador to the United Nations said Sunday that she could not confirm those reports but expressed concern about the prospect of Russian-organized "concentration and prisoner camps." 🔗 Read more at our link in bio. 📸: Aris Messinis, @gettyimages; Bernat Armangue, @apnews