UN: NZ PM at centre of Russia, US debate

New Zealand Prime Minister John Key has presided over an intense showdown in the United Nations Security Council as the US and Russia tussled over the bloody conflict in Syria.

The meeting was scheduled by Mr Key weeks ago, but became a crucial gathering on Wednesday following carnage in recent days including an attack on a convoy of trucks carrying food and medical aid and a bungled coalition bombing raid involving Australian aircraft that killed at least 60 Syrian soldiers instead of targeting Islamic State fighters.

US Secretary of State John Kerry and Russian Foreign Minister Sergei Lavrov tossed blame on each other, as well as other parties, for the failure of a ceasefire in the war-torn nation.

"New Zealand has convened today's high level meeting on Syria for one simple reason," Mr Key told the Security Council.

"No other issue more urgently demands the attention of world leaders.

"The Syrian civil war is the most devastating conflict of the 21st Century."

New Zealand, a non-permanent member of the Security Council for a two year term, holds the rotating presidency in September.

Mr Kerry said the bombing of the aid convoy near Aleppo that killed 20 people "raises a profound doubt if Russia" and Syrian President Bashar al-Assad's regime could live up to an agreement recently signed in Geneva to reduce violence in Syria.

Mr Kerry said the US and coalition partners quickly admitted to mistakenly bombing Syrian troops on Saturday, but argued it was different to the targeting of the aid convoy.

He said independent witnesses reported seeing fighter jets above the convoy and only Russia and Syria had aircraft in the area.

"But I got to tell you, people running around with guns on the ground, from the air, is a very different thing to trucks in a convoy with big UN markings all over them," Mr Kerry, comparing the coalition's accidental bombing to the aid convoy attack, said.

Mr Kerry also chastised Russian officials for offering varying explanations for the aid truck bombing, including blaming a mortar attack by militants and fires inside the trucks.

"The trucks, food and medicine just spontaneously combusted?" Mr Kerry asked.

"Anybody here believe that?

"This is not a joke.

"We are in serious business here."

Mr Lavrov said the attack on the convoy was an "unacceptable provocation" that took place in territory controlled by forces opposing the Syrian government.

"We insist on a very thorough and impartial investigation on the attack of the humanitarian convoy," Mr Lavrov said.

"Many said it could have been a rocket or artillery shelling, that's what the initial reports were.

"Then helicopters, war planes were mentioned.

"So I think we need to refrain from emotional reactions."

Mr Kerry said a mortar could not have caused the damage to the convoy.

Mr Kerry called for an immediate grounding of aircraft in "key areas" to allow humanitarian aid to flow and for all parties to cease support for any groups sabotaging attempts for peace.

He still held out hope for a genuine ceasefire.

"The future of Syria is hanging by a thread," Mr Kerry said.