"Wael Alwan, the spokesman for one of the main rebel groups in eastern Ghouta, Failaq al-Rahman, said Russian Federation was "insisting on military escalation and imposing forced displacement" on the people of eastern Ghouta, which he called "a crime".
Interviews with Eastern Ghouta civilians indicate that they do not trust the Syrian army, and believe that if they try to leave, the Syrian army will kill them.
Syrian government forces used chemical weapons against insurgents in eastern Ghouta, including chlorine three times in July, and in Harasta on the western edge of the zone in November, the report said.
A United Nations convoy delivered food and medicine to the town of Douma on Monday, but aid agencies say Syrian authorities blocked numerous health supplies, including trauma and surgical kits as well as insulin.
Meanwhile, state news agency SANA renewed accusing the rebels of preventing the civilians from leaving rebel-held areas in Eastern Ghouta toward the government areas through the Wafidin crossing northeast of Damascus. An aid convoy reached the area this week but government officials had stripped out most medical supplies.
The offer, which would allow rebels with personal weapons through a secure corridor, could pave the way for a deal by which the opposition would surrender its last major stronghold near Damascus to Mr Assad.
A United Nations convoy delivering the first aid since February to the town of Douma was forced to cut short its mission and left after almost nine hours amid shelling.
"But this is the first incident where we have been able to nail it down to a particular Russian plane and be able to investigate on the ground what took place", he added.
As Eastern Ghouta battle has entered a crucial stage, the Syrian Arab army continued to capture more territories after militants were ousted from nearly 40% of Ghouta.
The Defense Ministry says the An-26, with 26 passengers and six crew members onboard, crashed Tuesday just 500 meters (1,600 feet) from the runway. United Nations officials have complained for years about such actions by the Syrian government.
In a small but welcome step, an aid convoy did enter Eastern Ghouta on Monday to great fanfare.
Aksoy said the camps would host a total of 170,000 people. There are a small number of al-Qaida-allied rebels in the region, and rebel forces use eastern Ghouta to launch attacks on Damascus, albeit with far less firepower than the regime deploys.
Turkey views the main Kurdish militia in Afrin as an extension of the Kurdish insurgency within its own borders.