Ukraine has vowed to make pro-Russian rebels pay after losing 23 servicemen in clashes across the separatist east, while Russia proposed a UN resolution demanding a ceasefire to Europe's deadliest conflict in decades.

The Ukrainian defence ministry said Friday the death toll included 19 troops killed in a hail of rockets fired from a truck-mounted Grad rocket launcher system -- a type of weapon both Kiev and Washington insist could only have been covertly supplied to the rebels by Russia.

The official spokesman of Ukraine's intensifying eastern assault added that 93 servicemen had sustained "wounds and contusions of varying severity".

"The rebels will pay for the life of every one of our servicemen with tens and hundreds of their own," Ukraine's Western-backed President Petro Poroshenko told an emergency security meeting.

"Not a single terrorist will avoid responsibility," he said. "Every single one of them will get their just desserts."

Friday's official toll is the highest since Poroshenko tore up a brief ceasefire with the rebels on July 1 and relaunched an offensive that managed to dislodge the militias from key eastern strongholds they had held since early April.

The military separately spoke of "eliminating" nearly 100 fighters in one of Ukraine's bloodiest days since the start of the crisis last November when anti-government protests spiralled into revolution and a protracted standoff with pro-Russian rebels.