The United Nations has stepped up demands the Syrian regime allow UN access to rebel-held Damascus suburbs hit by an apparent poison gas attack.
At the same time, activists say they are trying to smuggle samples from victims to UN chemical weapons inspectors.
Opponents of Bashar al-Assad's regime say they have been in contact with the specialist UN team already in Damascus.
They say they are sending tissue samples by couriers seeking to get into the government-held city centre to deliver them to the inspectors.
The regime denies responsibility for the chemical attack that rebels say killed hundreds of people. It says terrorists were responsible.
Russia, Syria's long-time ally, has joined the calls for the government to cooperate with the UN, saying it must guarantee safe access for the investigators.