US Secretary of State John Kerry has claimed that the ceasefire in Syria “is not dead” following an attack on an aid convoy that killed around 20 people near Aleppo.

The Syrian Arab Red Crescent (SARC) has condemned the strike that killed around 20 humanitarian volunteers and one staff member, calling it “totally unacceptable”.

The UN and Red Crescent convoy was delivering aid supplies to Uram al-Kubra, west of Aleppo city, when it was struck on Monday night.

At least 18 of the 31 trucks in the convoy were hit in the strike, which is believed to have been carried out by either Syrian or Russian forces. Russia has denied that its planes carried out the strike, and Syria has denied deliberately targeting the convoy.

Mr Kerry – who personally negotiated the truce during months of intensive diplomacy with Russia – spoke about the crumbling ceasefire after emerging alongside Russian Foreign Minister Sergei Lavrov from a meeting of foreign ministers of 20 countries, gathered to discuss Syria in New York on Tuesday.

The United Nations peace envoy, Staffan de Mistura, said the ceasefire was in effect until its co-sponsors Moscow and Washington declared it over, and neither had done so at Tuesday’s meeting.

The US State Department said the ministers agreed at the meeting of the International Syria Support Group to continue pursuing the ceasefire under the US-Russian plan.

Syria’s army had declared the initial ceasefire period over on Monday, hours before the attack on the convoy which has been widely condemned.

“Failing to respect and protect humanitarian workers and structures might have serious repercussions on ongoing humanitarian operations in the country, hence depriving millions of people from aid essential to their survival,” Peter Maurer, the International Committee of the Red Cross (ICRC) President said in a statement on Tuesday.

“Today, the Red Cross and Red Crescent is in mourning.”

The Russian Defence Ministry said in a media conference that intelligence services had looked at drone footage from the incident, and did not see evidence of munitions hitting the convoy.

“Everything shown in the video is the direct result of a fire which mysteriously began at the same time as a large scale rebel attack on Aleppo,” Russian defence ministry spokesman Igor Konashenkov said.

Supplies are left strewn across the ground in Uram al-Kubra, where around 20 humanitarian volunteers were killed in an attack (Getty) (Getty Images)

The US made it clear on Monday night that it holds Moscow responsible for the deaths regardless.

“We don’t know at this point whether it was the Russians or the regime. In either case, the Russians have the responsibility certainly to restrain – refrain from taking such action themselves, but they also have the responsibility to keep the regime from doing it,” a US State Department statement said.

A Red Crescent warehouse and health clinic were also seriously damaged, and aid supplies for thousands of people were destroyed. A video from volunteer rescue group the Syrian Civil Defence, or the White Helmets, shows several vehicles and buildings on fire as ambulances arrive at the scene.

A Civil Defence member works to put out a fire after an air strike on the rebel held Uram al-Kubra town, western Aleppo city (Reuters)

The UN humanitarian aid agency has said all planned aid drops in Syria have been suspended in the wake of the attack.

UN humanitarian chief Stephen O’Brien said all warring parties had received notification of the convoy, which was carrying aid for about 78,000 people, warning that if the volunteers and aid workers were deliberately targeted “it would amount to a war crime”.

The attack comes as the seven-day ceasefire in the Syrian civil war expires. The truce between the Syrian opposition and government forces has already been severely tested by multiple violations, including President Bashar al-Assad’s refusal to let aid enter Aleppo as per the terms of the deal.

The Uram al-Kubra convoy was the first to be granted permission to proceed after six days of delays. The area has not received humanitarian supplies since July 2015.

Damaged Red Cross and Arab Red Crescent medical supplies are seen in a warehouse (Getty) (Getty Images)

Relations were already strained between the US, which backs some rebel groups in Syria, and Russia, an ally of the Syrian government, after a US coalition-led air strike near Isis territory killed at least 62 government soldiers on Saturday.

US officials acknowledged there might no longer be any agreement left to salvage after the convoy attack. If the truce is abandoned, it would most likely wreck the last hope of any breakthrough on Syria before the administration of President Barack Obama leaves office in January.

A senior Obama administration official said of the ceasefire: “We don't know if it can be salvaged”.

“At this point the Russians have to demonstrate very quickly their seriousness of purpose because otherwise there will be nothing to extend and nothing to salvage,” the official, who spoke to reporters on condition of anonymity, added.

A burnt out vehicle is abandoned in the road after the fire (AP)

Elsewhere at least 20 civilians, including a one-year-old girl, were killed in fresh air strikes on rebel-held parts of Aleppo city and surrounding areas on Monday, according to the UK-based Syrian Observatory for Human Rights. Russia said government positions in southwest Aleppo came under attack from militant groups, including a massive barrage of rockets.

The week-old ceasefire had brought a brief respite to at least some parts the war-torn country.

Foreign Minister Boris Johnson said that all members of the International Syria Support Group backed continued efforts by the US and Russia to adhere to the original ceasefire deal, and that the group will meet again to discuss the matter further.