America’s normally mild–mannered top diplomat, Secretary of State John Kerry, has angrily blasted Russia at the UN Security Council in a session called to discuss Syria.

In a strongly worded speech where he expressed incredulity over Russia’s various explanations over the bombing of an aid convoy, he called for all planes to be grounded over “key areas”.

He told the council the future of Syria is hanging by a thread.

Secretary @JohnKerry's remarks at the Council Session on #Syria: https://t.co/IAKr7AFwfG#UNGA pic.twitter.com/BW0FH1xB2K

— Department of State (@StateDept) September 21, 2016

As he spoke, Syrian rebels and pro–government forces were battling each other on major front lines near Aleppo and Hama, and air strikes have reportedly killed a dozen people including four medical workers.

As far as the US is concerned, Russia was responsible for the bombing of a humanitarian aid convoy near Aleppo that killed about 20 civilians and has outraged the world.

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

Russia denies responsibility – giving explanations 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.”

This is a moment of truth in #Syria, for Russia & the regime, for opposition, for international community. Cannot let spoilers prevail.

— John Kerry (@JohnKerry) September 21, 2016

Mr Kerry said the convoy bombing “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.

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.

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.

The Russian Defence Ministry claims a US Predator drone was spotted in the area several minutes before the bombing.

The UN has since suspended aid deliveries as the ceasefire that came into effect nine days ago collapses.

New Zealand called UN meeting

New Zealand Prime Minister John Key presided over the intense showdown as the US and Russia tussled over the bloody conflict.

The meeting was scheduled by Mr Key weeks ago, but became a crucial gathering on Wednesday following carnage in recent days.

As well as the aid attack there was a bungled coalition bombing raid involving Australian aircraft that killed at least 60 Syrian soldiers instead of targeting Islamic State fighters.

“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.

Here is the link to the UN’s web TV broadcast of the session.

– AAP with agencies