Russian state television showed a video claiming to show dozens of Ukrainian soldiers who surrendered to rebel forces in the besieged town of Debaltseve in Ukraine's east.
The soldiers were shown unarmed as they were walking in one column carrying their personal belongings and wounded servicemen on makeshift stretchers.
A rebel commander was heard promising to the soldiers that they would be respected and no one would beat or torture the surrendered military.
Ukrainian President Poroshenko said soldiers of one of Ukrainian division fighting in Debaltseve were captured by rebels after they ran out of weaponry.
Ukrainian government forces were pulling out of an encircled Debaltseve on Wednesday after a fierce assault by Russian-backed separatists which Kiev and Europe said violated a crumbling ceasefire.
President Petro Poroshenko said more than 80 percent of his troops had left the rail hub following a heavy bombardment and street-by-street battles.
The rebels say the ceasefire, negotiated by Ukraine, Russia, Germany and France at a summit in Belarus last week, does not apply to Debaltseve, which links the two rebel-controlled regions of eastern Ukraine, Donetsk and Luhansk.
There was little hope when the deal was signed last week in the Belarussian capital Minsk by the rebels, Ukraine, Russia and the OSCE security watchdog that it would hold for long, but its seeming swift collapse has surprised many.