Since the week-long truce brokered by Moscow and Washington earlier this month in an attempt to end the five-year war was forced to end on Monday, the US and Russia have persistently blamed each other for not doing enough.
The US expressed outrage at an attack on a convoy carrying humanitarian supplies.
The White House said all information indicates an airstrike hit the convoy.
"We hold the Russian government responsible for airstrikes in this space, given that their commitment under the cessation of hostilities was to certainly ground air operations in places where humanitarian assistance is flowing," White House National Security Adviser Ben Rhodes said.
Russia reacted furiously to the accusations. Russia's Foreign Ministry said it was watching "with indignation and anger" at attempts by "protectors of terrorists and bandits" to blame Russia or Syria for the attack.
And its Defence Ministry released drone footage, showing damage to the UN humanitarian convoy did not appear to come from an airstrike.
And a pickup truck with an attached mortar belonging to militants was accompanying the convoy.
This is not the first time that both side trade accusations recently.
"This said, even by Russia's standards, tonight's stunt, a stunt replete with moralism and grand-standing is uniquely cynical and hypocritical," US Ambassador to the UN Samantha Power said.
"As I was talking in the Security Council, sharing our analysis and frustration over the situation of Syria, Ambassador Power chose to talk to you.... the first thing she said, she was not interested in what I had to say because what I was saying was a stunt. In all my years in international life, which is over forty years, I've never seen such an extraordinary display of American heavy-handedness as we are witnessing today," Russian Ambassador to The UN Vitaly Churkin said.
After a US-led coalition airstrike killed over 60 Syrian soldiers in the northeastern Syrian city of Deir el-Zour, both ambassadors to the UN pointed fingers at each other.
But how could the ceasefire extend if the two side can not keep their own promises.
