Russian forces have advanced over a key waterway in the eastern Ukrainian stronghold of Chasiv Yar, a Ukrainian military official said, marking a setback for Kyiv’s embattled forces. The town of Chasiv Yar, which had an estimated pre-war population of around 12,000 people, sits on a strategic hilltop and its capture would likely speed Russian advances deeper in the war-battered Donetsk region. “The enemy managed to break into our line of defense, but there is no critical failure and we are not about to lose Chasiv Yar. Fierce fighting continues now,” a spokesman for Ukraine’s 24th brigade told…