UKRAINIAN forces have regained more ground but sustained further casualties in clashes with separatists, while two Western allies urged Russia's Vladimir Putin to exert more pressure on the rebels to find a negotiated end to the conflict.

The Ukrainian military says it plans to deliver a "nasty surprise" to the heavily-armed separatists who have dug in at Donetsk, a city of 900,000 people, after being pushed out of their bastion in Slaviansk.

But casualties mounted on the Ukrainian side with the deaths of three more Ukrainian soldiers in two attacks in different parts of the east.

In further international diplomacy to end the worst Russia-West crisis since the Cold War, French President Francois Hollande and German Chancellor Angela Merkel yesterday urged Mr Putin by telephone to "exert all necessary ­pressure" on the separatists to bring them to the ­negotiating table.