Russian forces have now fully withdrawn from northern Ukraine to Belarus and Russia, British military intelligence said on Friday.
At least some of these Russian forces will be transferred to East Ukraine to fight in the Donbas, the Ministry of Defence said on Twitter.
The forces will require replenishment before being deployed further east, with any mass redeployment from the north likely to take at least a week, the ministry added.
The ministry said Russian shelling of cities in the east and south continues and Russian forces have advanced further south from the city of Izium, which remains under their control.
Reuters could not immediately verify the report.
(Reporting by Juby Babu in Bengaluru; Editing by Jacqueline Wong)