Ukraine Air Assault ForcesRussian forces advanced further in their efforts to retake the Kursk region on Monday, threatening to encircle thousands of Ukrainian soldiers just as Kyiv prepared for talks with top U.

Russian special forces walked inside a gas pipeline to strike Ukrainian units from the rear in the Kursk region, Ukraine’s military and Russian war bloggers reported, as Moscow claimed fresh gains in its push to recapture parts of the border province that Kyiv seized in a shock offensive.

A surprise Russian assault through a gas pipeline, along with a major offensive, is quickly making Ukraine's hold on Kursk untenable

Ukraine’s presence in Russia’s Kursk region has deteriorated sharply, with the advance threatening Kyiv’s sole territorial bargaining counter at a crucial time in the war.

The front line inside Ukraine has become more static, Ukrainian soldiers say, even as Russia regains ground in its own Kursk region.

On Saturday, reports emerged that Russian troops had taken an unusual approach to trying to get behind Ukrainian lines in Russia’s Kursk region — crawling through a defunct section of a pipeline that once carried Russian gas to Europe via Ukraine.

Pro-Russian war blogger Two Majors said a major battle was under way for Sudzha and that Russian forces had surprised Ukrainian soldiers by entering the area via a gas pipeline.

By Guy Faulconbridge MOSCOW (Reuters) -Russian special forces crept miles through a major gas pipeline near the town of Sudzha in an attempt to surprise Ukrainian forces as part of a major offensive to eject Ukrainian soldiers from the western Russian region of Kursk,