Britain and France have addressed the UN Secretary General Ban Ki-moon with allegations that Syria has used chemical weapons on multiple occasions since December, according to reports emerging from top diplomats and officials.

The message came in the form of a letter, claiming that soil samples, witness interviews and statements from opposition sources support the idea that nerve agents had been used in and around Aleppo, Homs and supposedly the capital, Damascus. The officials chose to speak on condition of anonymity.

The case revolves around the supposed find of an agent “similar to sarin” in a soil sample, though it has not been revealed where the sample came from or what kind of chemical it is exactly.

President Assad’s administration has repeatedly denied the allegations, insisting that the rebels were behind the Aleppo attack on March 19, which took the lives of 26 people, including Syrian soldiers.

The European diplomats are hoping to prove that any damage inflicted upon the Syrian army was a case of friendly fire, in which a government shell supposedly missed its target.

A day after the alleged attack, Syrian envoy to the UN Bashar Jaafari called for an “impartial” probe to confirm the use of chemical weapons by the opposition, an idea backed by the Russian government. The UN chief agreed to the request, but the effort has since been marred by a disagreement over the scope of the probe, with Britain, France and the US insisting on a wider investigation throughout Syria. The UN inspectors have still not been given access.

The international body has asked Britain, France and Syria to give more detailed information and additional cooperation on the matter. UN officials say an inspection team will probably be sent to Britain to examine the sample in question, and that refugee testimonies from around the camps outside Syria will be gathered. 

Syrian government officials and military personnel visit a victim of chemical weapons at a hospital in Aleppo, March 21, 2013. (Reuters/George Ourfalian)

Following the Aleppo incident, President Obama warned that any use of chemical attacks by the Assad government would constitute crossing a “red line” and added that he had “instructed [his] teams to work closely with all other countries in the region and international organizations and institutions to find out precisely whether this red line was crossed.”

The director of US national intelligence, James Clapper Jr. added that all allegations are being evaluated. “We receive many claims of chemical warfare use in Syria each day, and we take them all seriously, and we do all we can to investigate them.”

France and Britain, however, took extra steps in a bid to disprove the Syrian government claims, according to one Western diplomat. “There was a strong effort to foil the Syrian government narrative and urge the secretary general not to fall into that trap,” he said.

Ban Ki-moon said on Wednesday that the investigation will continue despite any obstacles, even without access to Syria itself. 

“I have been urging the Syrian government to show flexibility in accepting the proposed modalities,” said the UN chief. “While awaiting consent from the Syrian government, the mission will proceed with its fact-finding activities. To this end, specific information has been requested from the governments concerned.”

Meanwhile, the UN has approved a plan for the delivery of humanitarian aid to affected regions in the country via “humanitarian corridors” from Syria’s neighbors. Previously aid had been distributed only to Damascus, from where it was distributed to the rest of the country.

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