Donetsk (Ukraine) (AFP) - Ukraine's army shelled the main rebel bastion of Donetsk Sunday as Russia called for a humanitarian ceasefire, which the West warned could be a pretext by Moscow to send in troops.
Shelling started early in the morning and continued throughout the day in the one-million strong eastern city, which pro-Russian rebels said was now surrounded by Ukrainian forces.
Ukraine's government reported four dead as troops and insurgents continued to clash for control of the industrial east.
Kiev also complained that Russian aircraft and drones were violating its airspace.
Amid a looming humanitarian crisis in rebel-held cities -- where residents were without water, power and with little food -- Russian Foreign Minister Sergei Lavrov made a renewed push for a truce to be able to bring aid to eastern Ukraine.
The West fears however that Moscow, accused of supporting the insurgents, may want to use an aid mission as cover to send troops into its ex-Soviet neighbour.
US President Barack Obama, German Chancellor Angela Merkel and British Prime Minister David Cameron have warned that any unilateral move by Moscow into Ukrainian territory would be "illegal" and "unacceptable".
- Donetsk under fire -
In the renewed shelling of Donetsk Sunday, city authorities reported that a home and a clinic north of the centre had been hit, injuring at least one person.
AFP journalists on the ground heard more than 20 explosions in the early morning and witnessed the assault continuing during the day.
A maternity hospital had its windows shattered while mothers and babies huddled in the cellar for safety, one AFP journalist reported. Several women said they gave birth in the belowground area.
Ukrainian forces have been forging on with an operation to wrest back control of the main rebel-held cities in the east, cutting them off from the Russian border.
Central Donetsk has been repeatedly targeted in recent days. On Sunday, Ukraine's military said it was "tightening its grip" on the city.
The head of the self-proclaimed Donetsk People's Republic, Alexander Zakharchenko, admitted earlier that the city was surrounded and urged a ceasefire to avert a humanitarian crisis there.
But on Sunday he made it clear that a truce would require a complete withdrawal by Ukraine's military from the east.
"As long as the Ukrainian army continues fighting, there cannot be a ceasefire," he said.
Heavy fire also continued in the second largest rebel-held city of Lugansk.
Ukraine's military reported three servicemen killed and 27 injured in the past 24 hours. Later, the interior ministry added another death and five more wounded to the toll.
National Security and Defense Council spokesman Andriy Lysenko said Ukrainian positions were under mortar fire from Russian territory, and two Russian helicopters and two drones had entered Ukrainian airspace overnight.
- 'Indispensable' ceasefire -
As the conflict worsened the humanitarian situation on the ground in the east, Russia's foreign minister said a ceasefire was "not only possible but indispensable".
Lavrov said Moscow was in talks with Ukraine, the Red Cross and UN aid organisations "on the need to send emergency humanitarian aid to the regions of Lugansk and Donetsk," adding that President Vladimir Putin was following the matter closely.
The West however suspects that Moscow wants to use a humanitarian mission as a pretext to send troops into Ukraine.
NATO says Russia currently has some 20,000 troops on the border.
Kiev already said late Friday that it had scuppered a Russian "humanitarian convoy" moving towards the border accompanied by troops and military hardware -- an allegation that Moscow denied.
In a round of telephone calls late Saturday, Obama, Merkel and Cameron agreed that any Russian intervention in Ukraine without Kiev's authorisation and even under the guise of a humanitarian mission would be "unacceptable" and "unjustified and illegal".
In a phone conversation with Merkel late Saturday, Ukraine's President Petro Poroshenko said he was ready to accept humanitarian aid for Lugansk and was already in talks with the Red Cross to organise a mission, but only if it is "an international one without any military escort."
More than 285,000 people have fled their homes in the east and over 1,300 have been killed in four months of what the Red Cross has already deemed a civil war.
In Lugansk, local authorities said residents were without power and running water for an eighth day, while fuel had dried up and food supplies were running short.
Pensions, salaries and social benefits were also not being paid as many banks in the region were closed.