Russia is throwing more units into its effort to take a key eastern Ukraine city, Western analysts say, after apparent setbacks that have slowed its dayslong onslaught. The attempt to storm Avdiivka, a heavily defended city that stands in the way of Moscow’s ambition of securing control of the entire Donetsk region, is Moscow’s most significant offensive operation in Ukraine since the start of the year, the UK defense ministry said on Tuesday.

The Kremlin’s push to claim Avdiivka comes after months of fending off Ukraine’s counteroffensive, which Kyiv launched some 16 months after Russia’s full-scale invasion. Both sides are looking for battlefield advantages ahead of winter. They are also looking to secure future weapons supplies for what is shaping up as a protracted war of attrition.