The United States has released statements saying it accuses Russia of being responsible for the attack on a humanitarian aid convoy near Aleppo on Monday.
US officials told the BBC that two Russian fighter jets were complicit in the heinous act.
The White House has called it an "enormous humanitarian tragedy".
Russia has vehemently denied any culpability in this incident, saying that it was a ground attack and not an air strike.
A spokeswoman for the Russian Ministry of Foreign Affairs said the US government made claims without any facts to back them up, adding: "We have nothing to do with this situation."
Some US officials wishing to remain anonymous said two Russian Su-24 jets were in the sky above the convoy at the precise moment it was hit in Urum al-Kubra.
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They consider the attack to be too sophisticated for the Syrian army to execute.
White House spokesman Ben Rhodes later said: "There could have been only two entities responsible, either the Syrian government or the Russian government.”
"In any event, we hold the Russian government responsible for airstrikes in this space."
The UN had earlier said it was "not in a position to determine whether these were in fact air strikes".
'Deal not dead'
The aid convoy lost 18 out of 31 trucks in the attack, and about 20 civilians were killed including a senior official of the Syrian Arab Red Crescent.
The UN has suspended all aid convoy movements in Syria following the attack.
The US and Russian diplomats in New York are frantically trying to recover a week-old ceasefire agreement between US and Russia which the Syrian army renounced a few hours before the attack on the convoy.
A meeting between the two parties have been scheduled for Friday.
The UN Security Council is also holding a high-level meeting discussing Syria on Wednesday.
'Blood on their hands'
Earlier, Ban Ki-moon, the UN general secretary, launched a tirade against the Bashar regime, accusing it of being responsible for the most civilian deaths in the five-year civil war.
The secretary general’s direct accusations surprised the UN General Assembly. He also said those who supported the opposing sides in the conflict had "blood on their hands".
"Many groups have killed many innocents, but none more so than the government of Syria which continues to barrel bomb neighbourhoods and systematically torture thousands of detainees."
He said other countries "that keep feeding the war machine also have blood on their hands".
The secretary general called the attack on the convoy: "sickening, savage and apparently deliberate" and called for those responsible to be held accountable.”
Syria responded by accusing the secretary general of flouting the UN charter.
"The words of Ban Ki-moon today on Syria are far removed from the provisions of the UN charter, which need to be respected by (the person) who occupies the role of secretary general," a foreign ministry statement said.
It said the UN had "failed in its role" to find solutions to international conflicts.
Humanitarian aid to besieged areas was a key part of the cessation of hostilities.
The president of the International Committee of the Red Cross, Peter Maurer, denounced the attack as a "flagrant violation of international humanitarian law" and said it was a borderline war crime.
The Syrian army and rebels have accused each other of widespread violations of the ceasefire agreement throughout the week.
On Saturday, a US airstrike killed 62 Syrian troops and injured 100 more and caused ISIS militants to overrun a Syrian base. The US has admitted the airstrike to be a “mistake”.