Ukrainian leaders are warning that the fate of the industrial heartlands in their country’s east depends on the amount of Western-supplied heavy weaponry that can be placed on the front lines in Donbas, as Russia presses on with its attempts to expand its control to Severodonetsk and other strategic cities. The entire area has come under heavy Russian fire, Serhiy Haidai, the Ukrainian governor of the eastern Luhansk region, which along with Donetsk makes up Donbas, said Friday. “Fierce street fights continue in Severodonetsk,” he said on the Telegram social-media platform, adding that key routes such as the road between...