Three Syrian opposition factions have agreed to cease fire in southern Damascus under an agreement brokered by Egypt and Russia that was not signed by the Syrian government, officials said.
The deal did not specify the area, but the three rebel groups control a pocket south of Damascus that is adjacent to areas controlled by the Islamic State group.
The deal would allow for humanitarian access but, unlike other similar agreements, would not involve the relocation of militants or residents.
Several such deals in recent years have involved bussing tens of thousands of people to the rebel-held Idlib province, in northwestern Syria.
The opposition has accused the government of forced displacement, charges denied by Syrian officials.
Egypt's state-run Mena news agency said the deal did not include the Syrian government.
Russia has been a main backer of President Bashar Assad's government, while Egypt has maintained intelligence and security cooperation with the government since 2013.
"The residents of this area will stay in their homes and this (deal) will lift the siege and cease the fire," Mohammed Alloush, of the Army of Islam rebel group, said by telephone.
He confirmed that the Army of Islam, Jaysh al-Ababil and Aknaf Beit al-Maqdis, which is linked to the Palestinian Hamas group, were part of the agreement.
Mena said the deal was signed at the intelligence headquarters in Cairo early Thursday and went into effect at noon.
It said the crossings south of Damascus will remain open for humanitarian access and said other opposition factions have been invited to join the cease-fire.
The deal came as Syrian opposition activists said government troops are pushing deeper into an IS stronghold in the country's east, the town of Mayadeen.
The Britain-based Syrian Observatory for Human Rights said clashes intensified early on Thursday, as government forces advanced into the western and northern neighbourhoods of Mayadeen, which lies on the Euphrates River.
The Observatory said troops were able to cut off the road linking Mayadeen and the town of Boukamal on the border with Iraq.
It added that IS brought in reinforcements from Iraq and elsewhere in Syria.
Opposition activist Mozahem al-Salloum said the fighting is fierce "in a way not seen before".
Omar Abu Laila, who runs a group that monitors developments in Deir el-Zour, said it will likely take time to drive IS out of Mayadeen, which is one of its last major strongholds.
Syrian troops reached Mayadeen on Saturday, after pushing south along the eastern banks of the Euphrates.