Boris Johnson has said that there was "strong" evidence that Russia carried out the air strike on the UN aid convoy that killed 20 people on 19 September.

As heavy air raids continued in Syria especially in and around Aleppo after the collapse of a week-long ceasefire, the UK Foreign Secretary spoke to reporters outside the UN Security Council meeting in New York.

Johnson said: "It's too early to say anything about criminality and to make conclusive judgements about responsibility, but put it this way: when you look at what happened to the aid convoy, there are only two possible culprits – only two forces capable of having carried out that strike, flying in that area.

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"They are the Syrians and the Russians, and we have our doubts about the Syrian capability to fly at night. So you are left with a pretty strong conclusion," he said, according to The Guardian.

Meanwhile, the US Secretary of State told the United Nations that the future of Syria was "hanging by a thread" and called for all planes in key parts of the war-torn country to be grounded.

John Kerry said that the attack on the aid convoy raised doubts over whether Russia and the Syrian government could live up to the terms of the ceasefire deal.

Criticising his Russian counterpart Sergei Lavrov's account of the collapse of the truce, Kerry said flights should stop to de-escalate the situation and give a chance for humanitarian assistance to flow.

"Listening to my colleague from Russia, I felt like I was in a parallel universe," Kerry said. The scale of the atrocities committed by the Syrian government, he said, meant "we can't just do business as usual.

Syria aid convoy bombed
A damaged truck carrying aid is seen on the side of the road near Aleppo in Syria after the UN aid convoy was bombed on 18 September 2016. John Kerry has called for the grounding of aircraft in key areas of the country Omar haj Kadour/AFP

"We can't just walk out of this room and say we go to back to ceasefire everyone knows won't work. Are we supposed to sit at a table and have happy talk with a government that does these things?" Kerry said.

The Russian defence ministry has said that a US drone appeared to be above the convoy several minutes before it caught fire.

General Igor Konashenkov said: "We are not jumping to unfounded conclusions. Only its owners know why the drone was in the area at the right time and what kind of tasks it was pursuing there."

A spokesperson for the International Committee for the Red Cross told IBTimes UK that pending an investigation, the attack on the convoy could be a war crime.

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