The United Nations says satellite images prove an air strike destroyed an aid convoy taking aid to rebel-held parts of Aleppo province, despite Russian claims the attack was a “well-prepared hoax”.

Russian authorities have also variously claimed that the lorries may have accidentally caught fire, been struck by the US “to deflect” from their own actions or been hit by rebels despite evidence that its own forces may have been responsible.

More than 20 people were killed in the attack in northern Syria, which incinerated 18 lorries in a joint UN and Syrian Arab Red Crescent convoy just hours after the end of a fragile ceasefire last month.

This satellite image released by the United Nations shows road damage and craters in the Sha'ar district of Aleppo, Syria, on 25 September 2016 (AP)

The US swiftly said Russian aircraft were thought to be responsible but the Kremlin denied the accusations and floated several alternative scenarios, which were dismissed by experts.

“With our analysis we determined it was an air strike and I think multiple other sources have said that as well,” Lars Bromley, research adviser at UNOSAT said on Wednesday.

Within hours of the release of satellite photographs on Wednesday, Russian state media was reporting claims by an unnamed group of “independent military experts” that the entire attack was a hoax.

Sputnik News cited damage patterns to support the sensational claim, publishing footage it said showed a vehicle transporting a mortar firing system past the aid convoy.

Russia denies Syria aid convoy attack with release of footage

“In summary of this preliminary analysis, we can conclude that we are dealing with a well-prepared staged or ‘fake’ attack,” it quoted the report as saying.

The supposed analysis is said to have been sent to the US but had its findings swiftly rejected.

The UN Secretary-General, Ban Ki-moon, is establishing an internal UN board of inquiry to investigate the attack and urged all parties to fully cooperate.

Previous analysis of debris found at the site of the attack on 19 September uncovered fragments of what appeared to be Russian fragmentation bombs.

American officials said two Russian Sukhoi SU-24 jets were in the skies at the exact time of the strike, following footage broadcast live by Russia Today showing a military drone monitoring the convoy’s progress.

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But Igor Konashenkov, a spokesman for Russia’s defence ministry, initially said there was no evidence the lorries had been struck by “ordnance”.

He claimed damage visible in footage was caused by the cargo catching fire, suggesting the convoy could be carrying military weapons and seeking to implicate the Nobel Prize-nominated White Helmets group of rescue volunteers.

The High Commissioner for Human Rights, Zeid Ra’ad al-Hussein, has accused Bashar al-Assad's government and its allies, including Russia, of presiding over a “ghastly avalanche of violence and destruction” in rebel-held districts of Aleppo.

“The attacks over the past 10 days have been the most intense the inhabitants of eastern Aleppo have endured since the conflict began, and not a single neighbourhood is now considered safe,” he said, specifically reminding Russia of its obligations under international weapons conventions.

“All seem to indicate that the ongoing operations are conducted in complete disregard for the most basic standards of international humanitarian law... the current operation by the Syrian government and its allies appears to be intended to force the surrender of fighters in eastern Aleppo by any means necessary."