The Ukrainian military said on Monday it was preparing for the "final stage" of taking back the city of Donetsk from separatists after making significant gains that have split rebel forces on the ground.

Spokesman Andriy Lysenko said Kiev's troops had now cut off Donetsk from the other main rebel-held city of Luhansk, 150 km away on the border with Russia.

"The forces of the anti-terrorist operation are preparing for the final stage of liberating Donetsk," Lysenko said. "Our forces have completely cut Donetsk off from Luhansk. We are working to liberate both towns, but it's better to liberate Donetsk first - it is more important."

The city, which had a preconflict population of 900,000, rocked to the crash of shells and gunfire over the weekend, and heavy guns boomed through the night into Monday from the outskirts of the city.

There was no definitive word on casualties from either side from the weekend assault by the government.

'Tightening the ring'

Government forces called on the rebels on Sunday to surrender. The separatists, who have proclaimed "people's republics" in the Russian-speaking east, have said there will be no end to fighting until Kiev withdraws its troops.

Though the government said it is tightening a cordon around the separatists in Donetsk amid changes in their leadership and desertions in their ranks, swathes of the east are still under rebel control, including the big border city of Luhansk, Horlivka to the north of Donetsk, and Makiyivka to its east.

UN agencies say over 1,100 people have been killed in four months of fighting between the separatists who seek union with Russia and troops representing a pro-Western government.

Although Lysenko said government forces had cut off the Donetsk-based rebels from their comrades in Luhansk, the key town of Krasny Luch, which lies between the two cities, is still not under government control, military sources in Kiev said.

Krasny Luch is a rail and road junction through which Russian military equipment has been transported to the rebels, Kiev said.

Ukraine and its Western allies accuse Russia of fomenting the separatist revolt, which erupted in April after Russia's annexation of the Crimea.

It said Russia is funneling tanks and missile systems to the rebels. Moscow denies involvement.

(China Daily 08/12/2014 page12)