Syrian activists say they are smuggling out body tissue samples from victims of an alleged chemical weapons attack outside Damascus and are trying to get them to a team of United Nations inspectors staying in a hotel a few miles away.
"The UN team spoke with us and since then we prepared samples of hair, skin and blood and smuggled them back into Damascus with trusted couriers," said activist Abu Nidal, speaking from the town of Arbin.
Some activists worry their efforts could be for naught - with little equipment and under constant shelling it is hard for them to prove their evidence has not be tampered with or damaged before it reaches UN experts.
The opposition accuses Syrian President Bashar Assad's forces of firing rockets before dawn on Wednesday loaded which poison gas in the midst of a fierce offensive on the rebel-held suburbs that ring the capital.
The army has been pummeling the area, known as the Ghouta region, since Tuesday night with air raids and artillery strikes that could hinder access to the sites and potentially damage evidence. Chemical weapons experts say every hour counts - the longer it takes, the more likely evidence can be covered up or tampered with.
Only a few activists said they were confident that they had a contact who would be able to hand their samples to the UN inspectors.
Most activists in the area who spoke to Reuters said they had also prepared samples to smuggle into the capital, but had little to zero contact with the UN experts and were unable to find a way to access the monitors inside their hotel.
"We're being shelled and on top of that Ghouta is surrounded by regime checkpoints. But even that isn't a problem, we can smuggle them out," said activist Abo Mohammed, from the suburb of Harasta.
"The problem is the location of the UN committee in the hotel. They're under heavy guard and government minders."
Opposition sources say that in addition to tissue samples they have taken photographs of bomb sites, written witness accounts, and samples of soil and animals in areas affected by the attacks.
An activist in Damascus who calls herself Alexia Jade confirmed that medics and activists in the suburbs have been trying to get samples out of the suburbs and were sending them to a secret location. She hinted there may be several organizations that the opposition would try to deliver the samples to, but would not give further details.
"Samples have been collected but the destination is confidential - and there may be more than one destination. The plan is to get the samples to someone who can actually do something about," she told Reuters on Skype.
Some medical centers in eastern Ghouta placed notices on Facebook calling on all doctors and medics that treated victims of the alleged attack to send tissue samples and reports to a centralized opposition medical center in the area in order to prepare them for use.
It asked for activists to maintain confidentiality as they prepared the reports.
Syria's uprising against four decades of Assad family rule has turned into a civil war that has killed more than 100,000 people.
Foreign powers have said chemical weapons could change the calculus in terms of outside intervention and have negotiated with Damascus to allow a UN team of experts to examine the site of three small-scale attacks where poison gas was allegedly used earlier this year.
The United Nations is now seeking to expand the group's mandate to allow them to investigate the most recent attack, whose death toll ranges from 500 to more than 1,000 people.
Syria has given no response to the demands. On Wednesday it denied using chemical weapons, calling the claims "illogical and fabricated."
Many activists in Ghouta said that while they were helping to collect samples, they were not hopeful their efforts would lead to any results from the United Nations.
"The last time we sent them evidence we had to smuggle it all the way north through Syria up to Turkey. And when investigators got it, they said the evidence could have been tampered with and was therefore not totally credible," said activist Abu Nidal.
"We have very little faith that the UN or the world will do anything for us no matter how hard we try to meet their demands. I personally think it's time to let the rebels handle this on their own."
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