The Organisation for the Prohibition of Chemical Weapons will be given access to an alleged chemical attack site in Syria on Wednesday, Russia says.
Experts arrived in Damascus on Saturday, but they have been unable to visit the nearby town of Douma because of “security issues” cited by Russia.
US officials have raised concerns that Russia, the Syrian government’s ally, might have tampered with the site.
The government insists the incident in Douma on 7 April was fabricated.
Opposition activists, medical organisations and rescue workers say more than 40 people were killed when aircraft dropped barrel bombs filled with toxic chemicals on the town while it was still held by rebel forces.
The US, UK and France say that, based on open source information and their own intelligence, they are confident chlorine and possibly a nerve agent were used.
On Saturday, they carried out missile strikes on three targets they said were “specifically associated with the Syrian regime’s chemical weapons programme”.
Syrian state media is reporting that inspectors have arrived in Douma but this has not been confirmed by the OPCW.
Russian and Syrian officials had cited “pending security issues” for not allowing inspectors to travel to the site of the alleged attack, the global watchdog’s director general said on Monday.
Syrian authorities had instead offered the inspectors the chance to interview 22 people who they said were at the location of the alleged attack and could be brought to Damascus for interviews, according to Ahmet Uzumcu.