The United States holds Russia responsible for the air strike on an aid convoy in Syria which was an "enormous humanitarian tragedy," White House deputy national security adviser Ben Rhodes says.
"We hold the Russian government responsible for air strikes in this space, given that their commitment under the cessation of hostilities was to certainly ground air operations where humanitarian assistance is flowing," Rhodes told reporters.
He said the United States prefers to continue with the ceasefire in Syria, but is concerned by Russia's failure to show good faith
Despite the military blame game over Monday's deadly attack, diplomats struggled to save the U.S.-Russian ceasefire agreement that took effect on September 12.
The incident, in which 18 trucks from a 31-vehicle convoy were destroyed, looked likely to deal a death blow to diplomatic efforts to halt a civil war now in its sixth year.
Two Russian Sukhoi SU-24 warplanes were in the skies above the aid convoy at the exact time it was struck late on Monday, two US officials told Reuters, citing U.S. intelligence that led them to conclude Russia was to blame.
Russia's foreign ministry spokeswoman denied the assertion, telling reporters at the United Nations the US administration "has no facts" to support the claim, adding: "We have nothing to do with this situation."
Earlier Russia, which denied its aircraft or those of its Syrian government allies were involved, had said it believed the convoy was not struck from the air at all but had caught fire because of some incident on the ground.
The Syrian Red Crescent said the head of one of its local offices and "around 20 civilians" had been killed, although other death tolls differed. The attack prompted the United Nations to suspend all aid shipments into Syria.
Senior officials from 23 nations emerged from a one-hour meeting on Syria at a New York luxury hotel with little more than an agreement to meet again, on Friday, about how to end a conflict that has killed hundreds of thousands and driven millions from their homes.
The UN Security Council is due to hold a high-level meeting on Syria on Wednesday.