The United States and Russia blamed each other for Syria’s failing cease-fire on Wednesday, illustrating why a fractured UN Security Council has been unable for more than five years to do anything to stop the Arab country’s civil war.

In a public session originally envisioned to enshrine Syria’s September 9 truce, world powers were left to rue the possibility of the conflict entering an even darker phase after a series of attacks on humanitarian workers.

Washington, Moscow and the council’s other nations all sought to revive the US.-Russian cease-fire deal, but seemed stuck on fundamental differences old and new: Who bears ultimate responsibility for the war and whose actions over the last days scuttled perhaps the best opportunity for peace?

"Supposedly we all want the same goal. I’ve heard that again and again," a clearly angry U.S. Secretary of State John Kerry told the council, referencing oft-repeated international objectives of a united, secular and democratic Syria.

"But we are proving woefully inadequate in … making that happen."

Kerry outlined a litany of US complaints against Syrian President Bashar Assad’s government and its chief backer, Russia.

He recited Moscow’s changing narrative over a deadly attack this week on an aid convoy that has included everything from claims of a justifiable counterterror strike to vehicles spontaneously combusting.

"This is not a joke," Kerry said, sharply criticizing those who engage in "word games" to dodge responsibility over questions of "war and peace, life and death."

Kerry offered one concrete suggestion to revive diplomatic hopes. Focused on protecting key aid routes in northern Syria, it was unclear if Russia and Syria would agree.

"To restore credibility, we must immediately ground all aircraft flying in those key areas in order to de-escalate the situation and give a chance for humanitarian assistance to flow unimpeded," he said.

The top American diplomat spoke just after Russian Foreign Minister Sergey Lavrov delivered his own set of barbs, underscoring the breakdown in trust in the 12 days since he and Kerry clinched a cease-fire agreement and a potential US-Russian military partnership against the Islamic State and al-Qaida.

The former Cold War foes and much of the international community hailed the outcome, only to watch it unravel amid an upsurge in violence that even included an accidental US strike that killed more than 60 Syrian soldiers.

Unlike Kerry, who stressed the importance of Assad’s government ending military operations against rebels and allowing in unfettered aid, Lavrov said the US had the biggest responsibility.

"The key priority is to separate the opposition forces from the terrorists," Lavrov said.

Responding to the wide criticism of the convoy airstrike, which American officials are blaming on Russia, Lavrov cited various possible explanations. Twenty civilians were killed when the Syrian Red Crescent convoy was struck.