US Secretary of State John Kerry has called for an immediate halt to airstrikes in Syria in an impassioned speech to the UN Security Council chaired by Prime Minister John Key.
Kerry was scathing of Russia's reaction to the bombing of a UN aid convoy in Syria on Monday, which killed 20 workers.
Key, in his opening remarks said Syria had become a "byword for failure" and UN Secretary General Ban ki-Moon began the speeches by saying "we are at a make or break moment" in the crisis.
Ban said he had asked his special envoy on Syria, Staffan de Mistura, to come up with a framework for direct talks between the Syria Government and opposition, a move supported by the US.
Kerry said Syria was the greatest human catastrophe since World War II.
"The future of Syria is hanging by a thread," he said.
Anyone who thought things could not get a lot worse in Syria were "dead wrong".
Unless efforts were made to revive the ceasefire, they would be back before the Security Council talking about more deaths and more refugees.
"The primary question is not what do we know but what are we collectively going to do about it."
He said stopping all airstrikes immediately was the only way to restore credibility to the process of finding a solution.
A ceasefire reached between Russia, which supports the Bashar al-Assad regime in Syria, and the United States literally went up in flames this week with an accidental airstrike against Syrian troops, killing 60, on Saturday, and the bombing of an UN aid convoy on Monday.
Kerry said the coalition had admitted it had struck Syrian forces and it had been "a terrible accident" that had been immediately acknowledged.
But there had been three different reactions from Russia, including a suggestion from the Ministry of Defence that the goods in the convoys had caught fire and spontaneously combusted.
"Anybody here believe that?"
Kerry said the rest of the world "can't just do business as usual".
"Are we supposed to sit there and have happy talk in Geneva?"
Kerry said the ceasefire deal was not perfect but he had yet to see anything better on offer.
Russian Foreign Minister Sergey Lavrov spoke before Kerry in more measured tones and for a lot less time.
He said monitors on the ground in Syria had counted 300 ceasefire violations in the week.
He said identifying al-Nusra - deemed a terrorist group along with Isis in the agreement - from other groups in Syria was difficult and that it could be time for the United Nations to revisit its list of terrorist organisations.
He also said Russia supported the efforts of de Mistura.
Key, in his opening remarks, said that after more than five years of violence, Syria had become a byword for failure: "Failure of the parties and their supporters to put peace, and the lives of innocent people ahead of self-interest and zero-sum politics; failure to respond to the crisis early to prevent this tragedy.
"And a collective political failure, including by this council, to do what must be done to end the conflict.
"It is critical that we rewrite this narrative of failure, and help set Syria on a path to peace.
"Let's be clear: no one will benefit from a continuation of this conflict.
"The Syrian Government, which bears responsibility for starting this war, cannot win.
"Nor can the many others whose support is allowing the conflict to continue.
"Ultimately, Syrians must reach agreement on their future government. But at this point it is clear that Syrians by themselves cannot end this war."