Russian forces have launched their anticipated offensive in eastern Ukraine, attempting to push through defenses along almost the entire front line early on Tuesday in what Ukrainian officials described as the second phase of the war.

Ukrainian President Volodymyr Zelenskyy said Russia had begun the "Battle of Donbas" in the east and a "very large part of the entire Russian army is now focused on this offensive."

"No matter how many Russian troops they send there, we will fight. We will defend ourselves," he said in a video address on Monday.