Ukraine said its forces were advancing on several axes in their counteroffensive but were struggling to counter Russian air and artillery superiority hobbling its assaults in the east and south. Now into its second week, Ukraine’s ambitious attempt to take back Russian-occupied land is proving to be a hard slog against dense minefields and well-prepared defenses. After Ukraine’s first probing attacks yielded mixed results, its forces have mostly paused their advances in recent days as commanders take stock of the past two weeks and analyze ways to punch through Russian lines without taking huge losses. Russia has taken advantage of...