During a swift counteroffensive in eastern Ukraine, President Volodymyr Zelensky claims his forces retook nearly 2,000 square kilometres.
If his most recent report is accurate, Kyiv's forces had made more than twice as much progress in just 24 hours.
Saturday saw Ukrainian forces rapidly push into strategic towns like Izyum and Kupiansk.
The Russian Defense Ministry confirmed the pullback, saying it would give its troops a chance to "regroup" in territory currently held by separatists supported by Moscow.
Russian officials stated that forces had been pulled out of Balaklyia, a third strategically important town, in order to "bolster efforts" on the Donetsk front.
Meanwhile, the leader of the Russian-installed government in the Kharkiv area has urged its residents to flee to Russia "to save lives."