Russia Says Study Suggests Syria Rebels Used Sarin Muzaffar Salman/Reuters As one member of the Free Syrian Army took his position inside the Umayyad Mosque in Aleppo on Monday to fight forces loyal to the embattled president, Bashar al-Assad, another rebel, at left, took a moment to snap a photograph with his cellphone. Russia said Tuesday that its scientific analysis of a suspected chemical weapons attack in Syria on March 19 showed it probably had been carried out by insurgents using sarin nerve gas of "cottage industry" quality delivered by a crudely made missile. The finding contradicted conclusions presented by Western nations, including the United States, that the Syrian government had been responsible. The Russian analysis, announced at a United Nations news conference by its ambassador, Vitaly I. Churkin, was based on what he said was evidence collected directly by Russian forensics specialists who had been permitted by the Syrian government to visit the site, Khan al-Assal in northern Syria. Mr. Churkin said he had informed Ban Ki-moon, the United Nations secretary general, who has been unsuccessfully pressing the Syrian authorities to permit his own team of chemical weapons experts to visit the country. Russia is the Syrian government's most powerful ally and has repeatedly blocked Western-led efforts at the United Nations Security Council to intervene in the Syrian conflict, suspecting that such a step would lead to possible military action that would remove President Bashar al-Assad by force. The Russians have said Mr. Assad and his antagonists should negotiate an end to the conflict, which began as a peaceful uprising against Mr. Assad in March 2011 and has evolved into a civil war. The Khan al-Assal attack, in which at least 26 people died, has been the focus of a propaganda battle between Mr. Assad's supporters and opponents, who have accused each other of using chemical munitions. Last month the Obama administration, which has called chemical weapons use a "red line" that could lead to American military action, said it had concluded that Syrian forces had deployed such weapons "on a small scale against the opposition multiple times in the last year," not only in Khan al-Assal but elsewhere, including the Damascus suburbs, in attacks that had killed 100 to 150 people. The American conclusion was based in part on indirectly procured soil samples and interviews with survivors, as well as the Syrian insurgency's lack of technical ability and materials to carry out a chemical weapons attack. The conclusion helped to form the basis for the Obama administration's decision to supply small arms and ammunition to the insurgents. Russia has from the beginning expressed doubt about the American conclusion, and Mr. Assad's government described it as a "statement full of lies." But Mr. Churkin's comments on Tuesday were the first detailed response by the Russians and offered an alternate explanation, although it was only for the March 19 attack in Khan al-Assal. Mr. Churkin said the Russian investigators had found evidence of crudely manufactured sarin, a nerve agent, delivered via an unguided projectile with a crude explosive charge - not the sort of munitions stockpiled by the Syrian military. "This was like a cottage-industry product, manufactured at a simple facility," Mr. Churkin said. He said, "There is every reason to believe that it was armed opposition fighters who used the chemical weapons in Khan al-Assal." Mr. Churkin did not release the Russian analysis, which he said was 80 pages long and buttressed with chemical formulas and graphs. The ambassador said he would be forwarding copies to his American, French and British counterparts. "I hope they find it persuasive," he said. The acting American ambassador, Rosemary A. DiCarlo, speaking to reporters later, said she had not seen the Russian analysis, "but we will certainly study it carefully when we do receive it." She reiterated the American demand that Syria allow the panel of experts appointed by the United Nations to enter the country and "investigate any and all credible allegations." Mr. Assad has insisted that the panel restrict itself to Khan al-Assal. The United Nations has estimated that at least 93,000 people have been killed and millions displaced in Syria since the conflict began, and has expressed growing alarm at the lack of security, shelter and food in large swaths of the country. The top official responsible for United Nations food aid to Syria said Tuesday that his relief teams were feeding at least three million people inside Syria, and that he expected the number to reach four million by October. The official, Muhannad Hadi, the Syria coordinator of the World Food Program, said in a telephone interview that the relief teams had been able to deliver aid to areas held by insurgents but must travel in armored vehicles. At the same time, he said, the relief teams have been unable to deliver food to some combat zones for months - even near one of its regional offices in the central city of Homs, a major battleground. "The situation in Syria is not ideal," Mr. Hadi said. There are people trapped in areas of conflict that we have not reached for a very long time.