DONETSK, Ukraine — The coffins sat in the loading bay of a local ice cream factory, filled with the battered bodies of fighters. They had gone to Ukraine to support the Donetsk People's Republic, and now they were bound for the border, heading home to Russia.

The men, who were described as volunteers, died earlier this week during a bloody battle for the Donetsk airport. Their corpses had since been stored in an industrial freezer. On Thursday afternoon they were packed in black plastic bags, placed in caskets lined with white fabric and stacked unceremoniously in the back of a truck.

There was no fanfare, no procession, no heroes' send-off. Instead, a shell-shocked work crew looked on while a man hand-painted the side of the truck with red crosses and "Cargo 200" — the Russian label for wartime casualties.

How the men — at least 30 Russian citizens, according to the Donetsk People's Republic — ended up at the front lines of Ukraine's brewing civil war remains a mystery. Neither their names nor their origins were revealed to the journalists who accompanied the cargo through rebel-held territory, a Ukrainian military checkpoint and up to the very edge of Ukraine. Тhe fighters' presence here and Russia's silence on their ominous return point to Russian President Vladimir Putin's precarious position as the conflict on his doorstep descends deeper into violence.

Since protesters seized the Donetsk regional administration building in early April and declared a people's republic in front of two Russian flags, joining the Russian Federation has been central, if not vital, to the movement's ambitions. Despite numerous appeals for assistance from the republic's leadership, Putin has refrained from officially recognizing the self-proclaimed government.

Ahead of the republic's referendum earlier this month on the region's independence from Ukraine, Putin suggested that the rebels reschedule. Last week, before Ukraine's presidential election, he announced the removal of Russian forces from the border — an apparent signal that a Russian invasion was no longer imminent. For the fighters who had been counting on Russian intervention, the month of May was one of disappointment.

"Putin promised help, and what did he do? He pulled back his forces from the border," said Sasha, a pro-Russian fighter from the rebel stronghold Slovyansk. "Putin betrayed what he promised."