"I can verify that the convoy was bombed," Lars Bromley of the UN's satellite observation program UNOSAT told a media briefing in Geneva on Wednesday.

His organization conducted extensive analysis of satellite imagery provided by the US State Department, before concluding that the September 19 attack - on a convoy unloading aid supplies at a warehouse - hailed from the air.

"For air strikes what you are usually looking at is the size of the crater that is visible, and the type of crater," Bromley said. "Basically air-dropped munitions are often much larger than anything you would fire from the ground."

Russia had previously said that its intelligence pointed to an attack from the ground - which would have raised the prospect of Syrian opposition involvement. Syrian rebels do not have an air force.

As well killing 20 people, the bombing at Urem Al-Kubra near Aleppo, left 15 others injured

Twenty people were killed and 18 of 31 aid trucks were destroyed in the bombing, which happened in a rebel-held town near Aleppo.

Convoy organizers had obtained clearances to travel through conflict areas from the Syrian government, rebels, as well as the US and Russia who operate military aircraft over Syria. Aid deliveries were temporarily stopped following the incident.

The US has said that Russian jets carried out the strikes,which also damaged an aid warehouse and a nearby medical center. US military officials have said that Russian and Syrian aircraft were in the area at the time of the attack.

But Moscow has denied it was responsible, instead blaming a blaze for the widespread damage.

New satellite images reveal extensive new damage to rebel-held areas of Aleppo in the past few days

Bromley also showed the latest satellite images, taken since the end of the latest failed ceasefire between the Syrian regime and opposition rebels.

He said the images showed "a great deal of additional damage," a reference to the Syrian government's newly-launched offensive to retake rebel-held areas of the northern city of Aleppo.

Bromley's comments also came just days after UN Secretary-General Ban Ki-moon promised a board of inquiry into the bombing.

UNOSAT, which reviews only commercially available satellite images, has observed the Syrian conflict since it began in 2011. Its analysis has revealed population movements caused by the fighting and damage to urban areas and key infrastructure.

mm/msh (AFP, AP, Reuters)