For the first several days of the invasion, Russia primarily concentrated its military forces on Kyiv, in the north, and Ukraine’s second-largest city, Kharkiv, in the northeast. But a concerted and in many ways more successful campaign is being waged in Ukraine’s south, along the coasts of the Black Sea and the Sea of Azov, a small, important body of water where Russia seeks full control.

As of Wednesday, Russian forces had captured the strategically important city of Kherson at the mouth of the Dnieper River, the first major city to come under Russian control. The fate of Mariupol on the Sea of Azov, an inland body of water that Russia and Ukraine share, also hung in the balance as Russian naval forces gathered in an apparent effort to mount an amphibious attack.

The carnage in Kherson was particularly extreme: Volunteers had been dispatched to gather up bodies, many of them unidentifiable because of tank and artillery fire, and bury them in mass graves, the city’s mayor, Igor Kolykhaev, said in an interview on Wednesday.