Russia is pushing back against Ukraine’s largest assault into Russian territory since the start of the war, sending troop reinforcements, establishing strict security measures in border areas and conducting airstrikes, according to the Russian Defense Ministry. One of the strikes on Ukrainian troops involved a thermobaric missile that causes a blast wave and suffocates those in its path, the ministry said.

But even as Russia has halted the quick advances made by Ukrainian troops who launched a surprise cross-border attack five days ago into the southwestern region of Kursk, Ukrainian forces seem to be holding ground. They claimed Saturday to have captured a small village in the neighboring Belgorod region, and analysts say their forces control most of the Kursk town of Sudzha, about 6 miles from the border.

Pasi Paroinen, an analyst from the Black Bird Group, a Finland-based organization that analyzes satellite imagery and social media content from the battlefield, said in an interview that evidence suggested that Moscow had been able to stall the major advances in Russian territory late in the week.