The White House says it holds Russia responsible for the air raids that hit 18 UN aid trucks in Aleppo on Tuesday
A day after the United Nations suspended all humanitarian aid into Syria, the United States and Russia wrangled over the blame for the air strikes that shattered the truce.
Washington held Moscow responsible for the air raid on the aid convoy that killed at least 20 in Syria.
White House deputy national security adviser Ben Rhodes said on Tuesday that Russia carried out the humanitarian tragedy.
"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.
Two Russian SU-24 warplanes were operating in the area where the aid convoy was struck in the Aleppo region late Monday, the official said.
Both Russia and Syria have denied involvement in the attack.
Russia's foreign ministry spokeswoman Maria Zakharova told reporters at the United Nations that the US administration "had no facts" to support its assertions.
UN spokesman Stephane Dujarric told reporters that at least 18 of 31 trucks in a UN and Syrian Arab Red Crescent (SARC) convoy were hit along with SARC warehouse.
The convoy was delivering aid for 78,000 people in the town of Urm al-Kubra in Aleppo Governorate, which is hard-to-reach ,he added.
Last week, the United States had apologised for attacking Syrian military position that killed at least 62 Syrian soldiers. The US had justified the air raid saying they believed they were targeting Islamic State posts.
The latest row has undermined international effort to impose a ceasefire in Syria.
The United States said it prefers to continue the truce but expressed concerns over Russia commitment.
US Secretary of State John Kerry insisted that efforts to revive the truce were "not dead."
(WION with inputs from agencies)