BERLIN—Russia says it has compiled a 100-page report detailing what it says is evidence that Syrian rebels, not forces loyal to President Bashar Assad, were behind a deadly sarin gas attack in an Aleppo suburb earlier this year.

In a statement posted on the Russian Foreign Ministry’s website late Wednesday, Russia said the report had been delivered to the United Nations in July and includes detailed scientific analysis of samples that Russian technicians collected at the site of the alleged attack, Khan al Assal.

Russia said its investigation of the March 19 incident was conducted under strict protocols established by the Organization for the Prohibition of Chemical Weapons, the international agency that governs adherence to treaties prohibiting the use of chemical weapons. It said samples that Russian technicians had collected had been sent to OPCW-certified laboratories in Europe.

The report itself was not released. But the statement drew a pointed comparison between what it said was the scientific detail of the report and the far shorter intelligence summaries that the United States, Britain and France have released to justify their assertion that the Syrian government launched chemical weapons against Damascus suburbs on Aug. 21. The longest of those summaries, by the French, ran nine pages. Each relies primarily on circumstantial evidence to make its case, and they disagree with one another on some details, including the number of people who died in the attack.

The Russian statement warned the United States and its allies not to conduct a military strike against Syria until the United Nations had completed a similarly detailed scientific study into the Aug. 21 attack. It warned that what it called the current “hysteria” about a possible military strike in the West was similar to the false claims and poor intelligence that preceded the United States invasion of Iraq.

“The Russian report is specific,” the ministry statement said. “It is a scientific and technical document.”

The statement also noted that the attention paid to the Aug. 21 had diverted attention from the March 19 incident, which was the reason UN investigators were in Syria when the Aug. 21 attack took place.

“Unfortunately, that investigation still essentially has not begun,” the statement said.

There was no immediate comment from the United States. Independent chemical weapons experts contacted by McClatchy said they had not had time to read the Russian document, which was released as Secretary of State John Kerry was appearing before the House Foreign Affairs Committee to make the Obama administration’s case for a retaliatory strike on Syria as punishment for the attack.

A UN team spent four days late last month investigating the Aug. 21 incident. The samples it collected from the site and alleged victims of the attack are currently being examined at OPCW labs in Europe. UN Secretary General Ban ki-Moon has urged the United States to delay any strike until after the results of that investigation are known.

Richard Guthrie, formerly project leader of the Chemical and Biological Warfare Project of the Stockholm International Peace Research Institute, who said he had not seen the original report, said the Russian statement on the makeup of the sarin found outside Aleppo, which the Russians said indicated it was not military grade, might reflect only that “there are a lot of different ways to make sarin.”

He added: “The messy mix described by the Russians might also be the result of an old sarin stock being used. Sarin degrades (the molecules break up) over time and this would explain a dirty mix.”

But he also agreed with the Russian conclusion that the rockets that delivered the sarin in the March 19 incident were not likely to have come from Syrian military stocks because of the use of RDX, an explosive that is also known as hexogen and T4.

“Militaries don’t tend to use it because it’s too expensive,” he said.

Another expert, Jean Pascal Zanders, raised a note of caution, questioning a Russian assertion that the sarin mix appeared to be a western World War II vintage.

“The Western Allies were not aware of the nerve agents until after the occupation of Germany,” he wrote in an email. “The USA, for example, struggled with the sarin (despite having some of the German scientists) until the 1950s, when the CW program expanded considerably.”

The Russian Foreign Ministry posted the statement shortly after Russian President Vladimir Putin had asked a Russian interviewer what the American reaction would be if evidence showed that Syrian rebels, not the Assad regime, had been behind a chemical weapons attack.

The report dealt with an incident that occurred March 19 in Khan al Asal, a town outside the city of Aleppo, in which 26 people died and 86 were injured.

The statement’s summary of the report said that neither the munitions nor the poison gas in the Khan al Asal attack appeared to fit what is possessed by the Syrian government. The statement said Russian investigators studied the site, sent the materials they found to study to OPCW sanctioned laboratories in Europe, and followed agreed-upon United Nations investigation standards.

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According to the statement, the report said the shell “was not regular Syrian army ammunition but was an artisan-type similar to unguided rocket projectiles produced in the north of Syria by the so-called gang ‘Bashair An-Nasr.’”

In addition, Russian investigators determined that the burst charge was RDX, which is “not used in military chemical munitions.”

The Russian analysis found soil and shell samples contained a sarin gas “not synthesized in an industrial environment,” the statement said. The report said the chemical mix did not appear to be a modern version of the deadly agent but was closer to those “used by Western states for producing chemical weapons during World War II.”

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