Corpses lie in the streets of Mariupol. Hungry people break into stores in search of food and melt snow for water. Thousands huddle in basements, trembling at the sound of Russian shells pounding this strategic port city. “Why shouldn’t I cry?” Goma Janna demanded as she wept by the light of an oil lamp below ground, surrounded by women and children. “I want my home, I want my job. I’m so sad about people and about the city, the children.” A humanitarian crisis is unfolding in this encircled city of 430,000, and Tuesday brought no relief: An attempt to evacuate civilians and deliver badly needed food, water and medicine through a designated safe corridor failed, with Ukrainian officials saying Russian forces had fired on the convoy before it reached the city. Nearly two weeks into the invasion, the Russians have advanced deep along Ukraine’s coastline in what could establish a land bridge to Crimea, which Moscow seized from Ukraine in 2014. Mariupol, which sits on the Azov Sea, has been surrounded by Russian soldiers for days. Mariupol, said Ukrainian Deputy Prime Minister Iryna Vereshchuk, is in a “catastrophic situation.” In other developments in the Russian invasion: — Poland offered to give all of its MiG-29 fighter jets to the U.S., apparently agreeing to an arrangement that would allow them to be used by Ukraine’s military. But Pentagon press secretary John Kirby later said the plan is not “tenable” and raises serious concerns for the NATO alliance. He said the U.S. would discuss it further with Poland. Read: Civilians flee Ukrainian city as 1 safe corridor opens — U.N. officials said that 2 million people have now fled Ukraine. — Russia’s economic isolation deepened as U.S. President Joe Biden announced a ban on Russian oil imports and Shell said it will no longer buy oil and natural gas from the country. Also, Adidas and McDonald’s said they are suspending their operations in Russia. For days, as Moscow’s forces have laid siege to Ukrainian cities, attempts to create corridors to safely evacuate civilians have stumbled amid continuing fighting and objections to the proposed routes. Ukraine has rejected Moscow’s offers of corridors that lead civilians to Russia or its ally Belarus. The Russian military has denied firing on convoys and charged that the Ukrainian side is blocking evacuation efforts. One evacuation did appear successful Tuesday, with Vereshchuk saying that 5,000 civilians, including 1,700 foreign students, had been brought out via a safe corridor from Sumy, an embattled northeastern city of a quarter-million people where overnight strikes killed 21, including two children.