Russia confirmed that its forces retreated from Izyum and Kupiansk. It said this was a strategic withdrawal to "regroup".
It has also said it will continue to target these areas with military strikes. The Russian army appears to have abandoned large quantities of equipment and ammunition during the withdrawal.
How much territory does Russia still occupy? Russia still holds about 20% of Ukraine, according to the ISW.
The areas are largely in the eastern Donbas region and in the south of mainland Ukraine, as well as the Crimea peninsula which Russia annexed in 2014.
The Donbas is a mainly Russian-speaking area, and after Russia seized Crimea in 2014, pro-Russian forces captured more than a third of the region. It created two so-called people's republics there.
Areas in the west of the country, including Lviv, have experienced missile attacks, but no attempt by Russian forces to take and occupy ground.
Russia refuses to recognise its invasion as a war, and says it is undertaking a "special military operation" in Ukraine.
The Kremlin said its operations would continue "until all the tasks originally set" had been achieved.
When launching the invasion in February, President Vladimir Putin said his goal was to "demilitarise Ukraine".
One objective was to ensure Ukraine didn't join the Western defensive alliance, Nato. Russia's initial aim was to overrun Ukraine and depose its government.
However, it now appears to have limited its ambitions to securing land in Ukraine's east and south. Both sides have suffered losses, although neither publish exact numbers.