Days before the leaders of Russia and the U.S. hold a summit meeting in Alaska, Moscow’s forces breached Ukrainian lines in a series of infiltrations in the country’s industrial heartland of Donetsk.

"What has been building up for the Ukrainians is fundamentally a manpower issue," a former senior Pentagon adviser told Newsweek.

Meeting of US and Russian leaders not expected to pave the way for a breakthrough given gulf between Moscow and Kyiv on key issues