Samples taken at the site where the chemical weapons were allegedly used indicate that it was rebels – not the Syrian army – behind the attack, Russia’s UN envoy Vitaly Churkin has said.

Russia has handed over the analyzed samples to the UN, he added.

“I have just passed the analysis of samples taken at the site of the chemical attack to the UN Secretary General (Ban Ki-moon),” Churkin said on Tuesday.

Evidence studied by Russian scientists indicates that a projectile carrying the deadly nerve agent sarin was most likely fired at Khan al-Assal by the rebels, Churkin pointed out.

“It was determined that on March 19 the rebels fired an unguided missile Bashair-3 at the town of Khan al-Assal, which has been under government control. The results of the analysis clearly show that the shell used in Khan al-Assal was not factory made and that it contained sarin,” he said.

Churkin added that the contents of the shell “didn’t contain chemical stabilizers in the toxic substance,” and therefore “is not a standard chemical charge.” The RDX – an explosive nitroamine commonly used for industrial and military applications – found in the warhead was not consistent with what the armed forces use.

According to Moscow, the manufacture of the ‘Bashair-3’ warheads started in February, and is the work of Bashair al-Nasr, a brigade with close ties to the Free Syrian Army.

Churkin stressed that unlike other reports which have been handed to the UN, the samples were taken by Russian experts at the scene, without any third party involvement.

More than 30 people died in the Khan al-Assal incident in the northern province of Aleppo in March. Damascus was the first to ask for the UN investigation, accusing opposition fighters of launching a chemical weapon attack. Syrian rebel groups denied the accusations, in turn blaming government forces.

However, the UN investigation has largely become stalled after a group of Western nations insisted on launching an inquiry into a separate case of alleged chemical weapons use in Homs in December 2012. The inquiry requires access to military objects, which Damascus has been unwilling to give.

The UN has also decided to exclude Russian and Chinese experts from the investigation team, with Syria protesting this decision.

So far, the UN commission of inquiry for Syria has not found any conclusive evidence proving that either side of the conflict used chemical weapons. This is despite several reports submitted by the US, UK and France, which claim to show that Syrian President Bashar Assad’s forces used such weapons.

Syria finds enough chemicals to ‘destroy the whole country’

The Syrian government invited chief UN chemical weapons investigator Ake Sellstrom and UN disarmament chief Angela Kane for talks in Damascus on Monday, announcing that a rebels-linked storage site containing piles of dangerous chemicals had been discovered.

“The Syrian authorities have discovered yesterday in the city of Banias 281 barrels filled with dangerous, hazardous chemical materials,” Syrian UN Ambassador Bashar Ja’afari said, adding that the chemicals were “capable of destroying a whole city, if not the whole country.”

The chemicals, which included monoethylene glycol and polyethylene glycol, were found in a storage site used by “armed terrorist groups,” Ja’afari explained. He said that Syria has started an investigation into the discovery.

The Syrian envoy expressed Damascus’ confidence that there will be “constructive negotiations with the Syrian officials in order to reach an agreement,” particularly in terms of “reference, mechanism, and time frame” of the UN mission.

Ja’afari  added, however, that one should not “jump to the conclusion” that the Monday invitation means that Syria would consider allowing the UN team access to sites beyond Aleppo.

UN Secretary-General Ban Ki-moon’s spokesman, Martin Nesirky, reacted by calling the invitation “a move in the right direction,” but did not say whether UN investigators would accept it. The UN has been demanding that Sellstrom’s team be granted access across Syria “without further delay and without conditions,” ordering the Aleppo investigation not to begin until those demands were reached.

‘No credible reporting that rebels used chemical weapons’?

Following Churkin’s announcement, both US and UK officials voiced their disbelief over any evidence suggesting that Syrian rebels used chemical weapons, stating they have yet been unable to see the whole report of Russia’s UN envoy.

The US has “yet to see any evidence that backs up the assertion that anybody besides the Syrian government has the ability to use chemical weapons, has used chemical weapons,” White House spokesman Jay Carney said.

When asked whether Washington had seen the Russian report, Carney replied that it had not.

The UK also voiced its skepticism regarding the report, stating that it didn’t believe the opposition could have obtained chemical weapons.

“We will examine whatever is presented to us, but to date we have seen no credible reporting of chemical weapons use by the Syrian opposition, or that the opposition have obtained chemical weapons,” BBC quoted a UK government spokesman as saying.