The UK’s Foreign Secretary Boris Johnson has said there was “strong” evidence that Russia carried out the air strike on the UN aid convoy that killed 20 people on September 19.

Speaking 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.

“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 International Business Times online reported that US Secretary of State, John Kerry, 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. He said 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.

“Listening to my colleague from Russia [Sergei Lavrov], 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”.

The Russian defence ministry 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.”