PARIS (AP) -- The Syrian doctors were reluctant at first to hand over the blood, urine and hair they had collected so carefully from sickened rebel fighters. But the team of French reporters from Le Monde persuaded the physicians, telling them they would get the syringes, tubes and sample bags to scientists who could analyze and identify the toxin, according to the newspaper's account published Wednesday.

It took the journalists about a month to cross government lines and get the deteriorating samples to French government scientists. It took France's foreign ministry a week to announce that traces of the nerve agent sarin had been detected, injecting new uncertainty into the debate in Europe and the U.S. over what to do about Syria.

France and Britain both announced Tuesday they had confirmed the use of sarin in Syria's conflict — something the U.S. and other governments have described as a game-changer in their calculations. A U.N. probe, also released Tuesday, said it had "reasonable grounds" to suspect small-scale use of toxic chemicals in at least four attacks in March and April in Syria.

According to the issue of Le Monde published Wednesday, the Syrian doctors had been carefully collecting the samples from sick rebels for some time, hoping to spirit them abroad for analysis because Syria lacks any independent labs to do so.

The team of journalists offered to take them — doctors were initially reluctant, but relented, handing over syringes of blood, tubes of urine and baggies of hair tainted with the unknown substance. At one point, the newspaper said, a minibus full of gassed fighters drove up to one of the medical centers and the treating doctor himself was overcome. One of Le Monde's photographers also fell ill with the symptoms, which included difficulty breathing, contracted pupils and vomiting.

In coming days as the team began heading out of Syria, rebel fighters handed over samples. Over the course of their stay in Syria, the paper said, the team of journalists were given more and more samples, many too degraded by lack of refrigeration to analyze. It took Le Monde about a month to get them out of Syria, the paper said.

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"Faced with the scope and frequency of the gas attacks, they thought it was vital to take out samples," the newspaper's editor, Natalie Nougayrede, said.

Nougayrede said the newspaper thought carefully before handing over the samples, but only one laboratory in France could carry out the work and it was affiliated with the government.

"We decided to hand over the samples on the condition that we would have access to the entire analysis," she said.

Jean-Philippe Remy, one of the reporters on the team, said he wasn't sure at the time that it was sarin, but he was fairly certain the Syrian government was responsible.

"I find it hard to imagine that the rebels could use weapons like this against their own fighters, given the panic it causes. As I've said, the two enemies are very close, and this supports the idea that small projectiles could be shot, that is to say, from the government positions," Remy said in an online chat with readers.