Ukraine’s military said on Monday it was preparing for the "final stage" of taking back the key eastern city of Donetsk from pro-Russian separatists, after government forces made significant gains that have split rebel forces on the ground.
The developments come as Ukraine said it had agreed on a Red Cross-led humanitarian aid operation with Russia, the European Union and other international partners to alleviate suffering in the rebel-held city of Luhansk.
Ukrainian officials took pains to specify that the government was behind the humanitarian convoy initiative and that Moscow was only one of several countries involved. They also said the mission had the backing of U.S. President Barack Obama.
Monday's announcement came hours after Moscow said it was dispatching a humanitarian convoy into eastern Ukraine. NATO fears Moscow would use any aid mission as a cover to save the rebels.
Meanwhile, Ukrainian government spokesman Andriy Lysenko said Kiev's troops have cut off Donetsk – the largest city in rebel-held eastern Ukraine – from Luhansk, 90 miles away on the border with Russia.
"The forces of the anti-terrorist operation are preparing for the final stage of liberating Donetsk," Lysenko told Reuters. "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 pre-conflict 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. One artillery shell hit a high-security prison on the city's western outskirts late on Sunday, killing one inmate and injuring three others, the city council said. More than 100 inmates escaped after the shell struck – though some returned later.
The prison break became possible after a substation providing the building with electricity was damaged, disabling the facility's alarm system. But Ukrainian security spokesman Lysenko blamed the prison strike on separatist fighters, saying "bandits in Donetsk shelled residential quarters and correctional facility No. 124."
Government forces on Sunday called on the rebels 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 says it is tightening a cordon around the separatists in Donetsk amid changes in their leadership and desertions in their ranks, large parts of the east are still under rebel control including the big border city of Luhansk, Horlivka to the north of Donetsk and Makiyivka to the east.
Lysenko said government forces had cut off the Donetsk-based rebels from their comrades in Luhansk, but 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 says.
Ukraine and its Western allies accuse Russia of fomenting the separatist revolt that erupted in April after Russia's annexation of Ukraine's Crimea peninsula. Ukraine says Russia is funneling tanks and missile systems to the rebels. Moscow denies involvement.
Donetsk, once a bustling metropolis, faces worsening shortages of food, water and fuel. Few civilians are on the streets, but groups of armed separatist fighters can be seen. There is relatively little traffic, with gasoline in short supply.
Those who have not left for the countryside are staying indoors. Banks are closed and pensions and social allowances are not being paid.
All sides recognize the seriousness of the humanitarian situation in eastern Ukraine, and Kiev and its Western allies fear that Russia will use the situation as a reason to move its forces into the country.
The geopolitical tussle over the future of the former Soviet state of 46 million has grown sharper since the July 17 downing of a Malaysian airliner in the eastern Ukraine conflict zone, with the deaths of all 298 passengers and crew. Kiev and its Western allies have laid the blame for the attack on the pro-Russian rebels. The separatists and Moscow say flight MH17 was downed as a result of Ukraine's military offensive.
A total of 568 Ukrainian troops have been killed during four months of fierce fighting, the Ukrainian military said. Another 2,120 servicemen have been wounded during the conflict, security spokesman Lysenko said.
Overall, the United Nations estimates that more than 1,300 people have been killed since fighting erupted in mid-April.
Al Jazeera and wire services