Ukraine's warring sides trade blame on school shelling

 Ukraine's warring sides on Thursday traded blame over the deadly shelling of a school sports ground in rebel-held territory that killed two teenagers as they played football.
Pro-Russian insurgents announced two days of mourning for the slain adolescents as Russian investigators launched a criminal case against Ukrainian forces.
But Kiev hit back saying that Kremlin-supported fighters were behind the deadly attack close to where fighting rages on for control of the ruined airport in separatist bastion Donetsk.
The fierce propaganda war over the latest slaughter in Ukraine's bloody seven-month conflict highlighted the difficulties of disentangling who is to blame for each killing.
Both sides have been accused of indiscriminately shelling populated areas by the United Nations and rights groups as the death toll for the fighting has reached over 4,000. Both sides deny the allegations.
At the shell-scarred playing field pieces of flesh remained strewn around the turf were the two boys were killed -- and four others injured -- in Wednesday's attack.
Local residents had placed several bouquets of flowers at the site in remembrance of the victims aged 14 and 18.
Anger was at boiling point as people vented their frustration against those -- usually government forces -- that they blamed for the killings.
"They should come here and see what they've done, how they've killed children," local inhabitant Vasily, 58, told AFP.
"We should scratch out their eyes and force them to live as we do under constant bombing."
- Experts arrive, blame flies -
The rumble of heavy shelling and unguided rocket fire echoed  around the district as government forces continued to cling on ferociously to the gutted international airport several kilometres away.
In the chaos and hatred swirling in east Ukraine there are very few organisations that are seen as neutral referees capable of fairly investigating any crimes.
Almost the only international observers in the region are from the Organisation for Security and Cooperation from Europe, which has been on the ground monitoring the fighting for months.
They said their experts were on Thursday at the site and trying to piece together what happened.
"They are starting work now, and will collect facts from what they can see," spokeswoman Iryna Gudyma told AFP.
But before any thorough probe could even be launched into the killings both sides were already lashing out at each other.
Rebel leader Boris Litvinov said the Ukrainian army was behind the deaths and accused Kiev of a "stream of lies" aimed at convincing people that the insurgents were shelling their own turf.
Meanwhile, Russia's Investigative Committee said they had opened up a criminal case against Ukrainian commanders, saying the attack was part of attempt to "wipe out the Russian-speaking population" in the war-torn region.
A Kiev military spokesman, however, rejected the claims and showed video and photos of the scene that they said proved the bombardment came from rebel-held territory.
Ukraine's security agency had opened its own criminal case into the incident, spokesman Andriy Lysenko said.