The United Nations has suspended all aid convoys in Syria after a devastating attack on its lorries near Aleppo on Monday.
The strikes, which witnesses said came from the air, came hours after Syria declared a week-old United States-Russia brokered cessation of hostilities at an end.
Russia and Syria have both insisted that their forces were not involved, BBC stated.
But UN chief Ban Ki-moon launched a stinging attack on the Syrian government, saying it had killed the most civilians in the civil war.
In unusually blunt language, Mr Ban said “powerful patrons… feeding the war machine, also have blood on their hands”.
US Secretary of State John Kerry, speaking alongside his Russian counterpart Sergei Lavrov, insisted the ceasefire deal was “not dead”, following talks on the sidelines of the UN General Assembly on New York on Tuesday.
UN Syria envoy Staffan de Mistura also said there was still hope but said delegates from the Syria Support Group had agreed it was in danger.
The attack at Urum al-Kubra destroyed 18 of 31 lorries and killed about 20 civilians, including a senior local official of the Syrian Arab Red Crescent, named as Omar Barakat.
Russian defence ministry spokesman Igor Konashenkov said that after studying video taken at the scene they “did not find any signs of munitions hitting the convoy”.
“Everything shown in the video is the direct result of a fire which mysteriously began at the same time as a large scale rebel attack on Aleppo,” he said.
The Syrian military, quoted by state media, said there was “no truth” to reports that the army had targeted the convoy.
A media activist who witnessed the attack told the BBC Arabic service that Russian reconnaissance planes had been spotted, apparently filming the passage of the convoy.
He said the first strike came at about 19:00 local time on Monday, when a helicopter dropped several barrel bombs. This was followed by rocket and machine-gun fire from aircraft, he said.