KRAMATORSK, Ukraine — Ukrainian soldiers, seeking to spread Russian forces thin, launched a counteroffensive on Sunday in Kherson, the key southern city that Moscow considered so securely under its thumb that it had introduced the ruble.
Ukraine’s push in Kherson came as its forces were desperately battling to hold off Russia’s efforts to conquer and cut off a strategic strip of Eastern Ukraine that is central to Moscow’s struggling war effort, and it had the effect of expanding the…