The Syrian government has agreed to allow UN inspectors to investigate allegations of a suspected chemical weapon attack near Damascus.
The team is to begin work on Monday. Activists say Syrian forces killed more than 300 people in several suburbs east and west of the capital on Wednesday.
UK Foreign Secretary William Hague warned that evidence could have been tampered with, degraded or destroyed in the five days since the attack.
Syria has blamed "terrorists".
State media reported that chemical agents were found in tunnels used by rebel fighters, and also that soldiers suffered "suffocation" in fighting around the suburb of Jobar.
State TV is meanwhile reporting that the governor of the central district of Hama, Anas Abdul-Razzaq Naem, has been killed in a car bomb attack.