(Repeats Thursday story with no changes)
* Separatists are facing Ukrainian government offensive
* Fallen fighters arriving at cemeteries in city of Donetsk
* Many of them are unidentified, hastily buried
By Maria Tsvetkova and Thomas Grove
DONETSK, Ukraine, Aug 21 (Reuters) - Pro-Moscow rebels in the Ukrainian city of Donetsk are taking such heavy losses in fighting with advancing government troops they no longer have time to give their comrades a proper burial.
That task fell instead on Wednesday afternoon to Igor Yegorov and his crew of three grave-diggers, dressed in track suit bottoms and vests, at the Sixth Capital municipal graveyard on the edge of Donetsk, eastern Ukraine.
A Soviet-designed Zil flat-bed truck backed into a corner of the cemetery with 12 coffins stacked two deep in the back, each one containing the corpse of a rebel fighter.
The cemetery workers approached the truck to unload the coffins, but hesitated, driven back by the smell of decaying flesh escaping through gaps in the crudely built coffins. Yegorov pressed them to hurry up.
"We need a gas mask here," said one of the workers.
"A gas mask won't help," said Valery, the driver of the truck that brought the coffins.
Two hours later, the burial was over. There was no ceremony, no rebel honour guard, and no relatives at the grave side. The grave-diggers lowered the caskets into graves, then covered them up using an old tractor with an earth-moving bucket on the front.
The new graves were marked with rough wooden plaques with a number. That was supposed to correspond to the dead fighter's name, but according to a manifest that was sent from the morgue and was shown to Reuters, the identities of eight of the 12 were unknown.
For several weeks now, the separatist rebels - which Kiev and its Western allies say are proxies for Russia - have been forced to retreat in the face of advances by a newly confident Ukrainian military.
Unlike the government forces, the rebels do not release casualty figures. The hasty burials, combined with accounts from fighters, provide a snapshot of the scale of the rebel losses, raising the question of how long they can keep fighting against the numerically superior Ukrainian forces.
The rebels' ability to hold on has a bearing on how soon an end comes to a conflict that has killed thousands of people, sparked a round of damaging sanctions, and dragged Russia's relations with the West to their lowest ebb since the Cold War.
Russia denies giving material help to the separatists.
The Sixth Capital cemetery, named after a nearby coal mine, is the only one in Donetsk that receives fighters' bodies for mass burials, with the first arriving on July 15, according to cemetery workers.
By Wednesday, 41 fighters had been buried there, including the 12 coffins brought in that day. A Reuters photographer who went back to the same cemetery on Thursday said he saw at least another 15 fighters being buried.
But those are only a fraction of the rebel dead. Local government officials said rebels were buried individually at all 28 cemeteries in Donetsk, and fighters spoke too of burying fallen comrades in the field.
One fighter, who gave his nom de guerre as "Americanets," or American, told Reuters on the outskirts of Donetsk on Wednesday that his unit had started out with 100 fighters.
"They've almost all died," he said, dressed in camouflage fatigues and black gloves with Gold's Gym insignia almost completely worn off them. "There's barely anyone left to fight."
"We pick up the dead, the remains of the dead, more like pieces of meat: a head there, a leg there," he said. "If they get hit by artillery, that's all we can do."
"We try to get in touch with the families if we know where they are or who they are, then they can come themselves, and collect the body and send it to the morgue."
"If we can't identify the remains or if we can't get the body out of the theatre of operations, then we have the give the body a field burial: we dig a pit and put the remains in."
The leader of another battalion said he was preparing to bury another 11 fighters in the next day, but it was getting difficult to pay for any funeral arrangements.
"We're trying to give them a burial, but money is getting tighter and tighter," he said, speaking on condition of anonymity.
Ukrainian officials say that about 600 combatants on their side have been killed in the conflict.
Ukraine's armed forces have around 120,000 personnel, though not all are front-line troops. In addition around 10,000 servicemen attached to the national guard, police and volunteer militias are involved in the fighting on the Ukrainian side.
It is impossible to establish how many fighters are on the rebel side.
Separatist leaders say they can win the war. Aleksander Zakharchenko, prime minister of the self-proclaimed Donetsk People's Republic, said last week reinforcements were arriving and a counter-attack was being prepared.
On the ground in Donetsk, most rank-and-file rebels say they are determined to keep fighting, but they acknowledge that the toll is getting heavier.
A fighter who identified himself by the nickname "Starets," or Elder, is responsible for arranging funerals for the Vostok Battalion, a rebel unit involved in some of the toughest fighting in and around Donetsk.
He said by his estimates about 10 rebels a day are killed in Donetsk, a figure that does not include casualties from heavy fighting outside the city.
"The circle has been tightening," he said. "We can expect more losses." (Additional reporting by Natalia Zinets in KIEV; Writing by Maria Tsvetkova and Christian Lowe; Editing by Giles Elgood)