Pro-Russian separatists in Donetsk have vowed to fight until the end as Ukrainian forces advance on the city.
They claim there is nowhere to retreat to and have built new checkpoints in a bid to slow the advances of government troops.
Ukrainian forces, fresh from taking Slovyansk at the weekend, have been fighting separatists at Karlivka, just 20km from Donetsk.
Their advance comes as Ukraine vowed to do its utmost to get one of its army pilots released from a Russian prison.
Nadia Savchenko was charged with complicity in the murder of two Russian journalists.
The pilot was involved in an attack on a separatist checkpoint, which left the journalists fatally wounded.