Russia launched its long-feared, full-scale ground offensive to take control of Ukraine’s east on Monday, attacking along a broad front over 300 miles (480 kilometers) long, Ukrainian officials said in what marked the opening of a new and potentially climactic phase of the war.

“The Russian troops have begun the battle for the Donbas,” Ukrainian President Volodymyr Zelenskyy announced in a video address. He said a “significant part of the entire Russian army is now concentrated on this offensive.”