KYIV, Ukraine, March 9 -- Russian special forces walked kilometers (miles) inside of a gas pipeline to strike Ukrainian units from the rear in the Kursk region, Ukraine's military and Russian war bloggers reported, as Moscow moves to recapture parts of its border province that Kyiv seized in a shock offensive.

Ukraine launched a daring cross-border incursion into Kursk i n August, in what marked the largest attack on Russian territory since World War II. Within days, Ukrainian units had captured 1,000 square kilometers (386 square miles) of territory, including the strategic border town of Sudzha, and taken hundreds of Russian prisoners of war.

According to Kyiv, the operation aimed to gain a bargaining chip in future peace talks, and f...