Russian troops advanced in September at their fastest rate since March 2022, the month after President Vladimir Putin ordered the invasion, according to open-source data.

“The Armed Forces of Ukraine are holding back one of the most powerful Russian offensives since the beginning of the full-scale invasion,” General Oleksandr Syrskyi wrote on the Telegram messaging app.

After failing to capture the capital Kyiv early in the war and win a decisive victory, Putin scaled back his war ambitions to taking the Donbas industrial heartland in Ukraine’s east, which covers the Luhansk and Donetsk regions.

Donbas has since become the war’s main theater, where some of the biggest battles in Europe for generations have taken place and where thousands of troops on each side have died.

On Saturday, Moscow said it has taken two more settlements along the Donbas frontline. In the week of October 20-27 alone, Russia captured nearly 200 square km (80 square miles) of Ukrainian territory, according to the Russian media group Agentstvo, which analyzed Ukrainian open-source maps.

The war is entering what Russian analysts say is its most dangerous phase as Moscow’s forces advance, North Korea sends troops to Russia and the West ponders how the conflict will end.

Ukraine’s President Volodymyr Zelenskyy has been traveling the world lobbying NATO countries to allow Kyiv the use of the long-range missiles they have provided to strike targets deep inside Russia.

Ukraine is bracing for what could be the toughest winter of the war after long-range Russian airstrikes destroyed what officials say is about half of its power generating capacity.