Russian forces made a sudden thrust in eastern Ukraine in recent days, as Russian leader Vladimir Putin seeks a battlefield advantage ahead of talks with President Trump on Friday. The infantry penetration, which officials and soldiers said stretched several miles deep near the Ukrainian city of Dobropillya, is a rare move in a war where defenses have gained the upper hand and Russia has struggled to add to the around 20% of Ukraine that it has occupied for much of its 3½-year invasion. Ukraine’s military said it was counterattacking in the area against what it said were small groups of...