The Syria cease-fire always seemed like it was destined for failure. And on Sunday the truce seemed to start to fall apart amid an airstrike on rebel-held neighborhoods of Aleppo. Rebels said a total of four airstrikes hit Aleppo on Sunday, marking the first raids in the city since the cease-fire officially began on Monday. The strike came shortly after Russia warned that the future of the truce was in doubt after the U.S.-led coalition killed more than 60 Syrian soldiers. The U.S. military has acknowledged that it may have struck Syrian troops in error.

The U.S. “relayed our regret through the Russian Federation for the unintentional loss of life of Syrian forces fighting ISIL,” a senior U.S. official told CNN.

The errant airstrike led to some of the harshest exchanges between Moscow and Washington in recent memory with lots of grandstanding at the United Nations as Russia called for an emergency meeting. The Russian government even went as far as to suggest that maybe the airstrikes weren’t a mistake. “The actions of coalition pilots—if they, as we hope, were not taken on an order from Washington—are on the boundary between criminal negligence and connivance with Islamic State terrorists,” Russia’s Foreign Ministry said in a statement.

Secretary of State John Kerry fired back in an interview with CNN saying that Russia needed to “stop the grandstanding, stop the showboating and get the humanitarian assistance going.” Although the truce was meant to stop the fighting long enough to deliver humanitarian aid to civilians, particularly in Aleppo, trucks piled with food were still waiting for the go-ahead from the Syrian government, reports the Washington Post.

Others went further as members of the Syrian government directly suggested the strike may not have been a mistake and were proof that the United States is helping ISIS in order to oust President Bashar al-Assad. “These attacks confirmed that the U.S. clearly supports the terrorism of Daesh,” Syrian state-run SAMA television said.

Australian Prime Minister Malcolm Turnbull acknowledged Sunday that Australian aircraft were involved in the airstrikes. “As soon as the coalition commanders were advised by the Russian command in the region that Syrian forces had been affected, the sortie was discontinued,” he said.