The deal will see 1,500 rebels and 6,000 civilians depart, according to the state-affiliated Military Media Center.
The convoy of buses from Harasta, their headlights blazing, was reminiscent of those ferrying defeated rebels out of eastern Aleppo in late 2016, following a similar agreement with the government.
"They are leaving toward Idlib with no return," said Rabieh Dibeh, correspondent for state-affiliated al-Ikhbariya TV, when the buses started moving.
The deal is modeled on others that have had rebels surrender swaths of territory around the capital and other major cities to the government. In all cases, the arrangements followed indiscriminate bombing campaigns against hospitals, markets and other civilian targets, driving thousands from their homes.
As Ahrar al-Sham rebels prepared to leave Harasta, thousands of civilians streamed out of other areas in eastern Ghouta that were still being bombed by the government.
Dozens of the civilians appeared to be wounded, some hobbling on crutches, another with an eye injury. Several children were seen crying in fear. A girl who appeared to be younger than 10, wearing a yellow dress, struggled to walk while carrying a toddler and some belongings.
The government assault has sparked a tide of people trying to escape the violence in the Damascus suburbs. Some have moved deeper into the rebel-held enclave, while about 50,000 others have crossed the front lines toward government-controlled areas.
The air and ground assault, which escalated Feb. 18, has seen the once- sprawling territory at the edge of the capital shrink to three disconnected rebel-held islands. That has made it only a question of when — not if — the Russian-backed government forces would recapture the entire region.
Also on Thursday, the media arm of Lebanon's Hezbollah group and an opposition activist group said the second-largest rebel group in eastern Ghouta has declared a cease-fire in order to negotiate leaving the area.
The rebel group Failaq al-Rahman will abide by a cease-fire as of midnight Thursday, according to Hezbollah's Al-Manar TV and the Britain-based Syrian Observatory for Human Rights monitoring group.
There was no immediate comment from Failaq al-Rahman. Hezbollah is fighting alongside Assad's forces.
The international medical charity Doctors Without Borders said the advancing government forces had captured or destroyed 19 of the 20 hospitals the group was supporting only a week ago. Medical workers were fleeing the approaching front lines, it said.
Rebels now hold only one-fifth of the territory they controlled a month ago in eastern Ghouta, according to the Observatory. But that territory includes several densely populated residential zones, including Douma, the largest town in the enclave.
Iyad Abdelaziz, a member of Douma's Local Council, said a civilian committee representing the town is in talks with the Russians to reach a settlement. He said the committee has presented a proposal to the Russians for their forces to enter the town, while residents stay in place and restore state institutions there. Abdelaziz said he did not have further details.
"Until now, there's been no response from the Russians, but today we received a reply of rockets and bombs," he said.
Commenting on Thursday's evacuations from Harasta, Douma-based Syrian opposition activist Haitham Bakkar accused the government of forcefully removing its opponents from some areas and replacing them with Assad supporters.
"This is a demographic change par excellence," he said.
Rebels and the government exchanged 18 prisoners ahead of the Harasta evacuation, according to pro-government media.
The 13 men released by the rebels identified themselves to the media outside Harasta as soldiers and civilians attached to the Syrian army who were captured in the fighting for the town. Crying in relief, they thanked God, the Syrian army and Assad for their freedom.
Monther Fares, a spokesman for the rebel faction Ahrar al-Sham, confirmed that his group's fighters were preparing to depart. Fares said the rebels agreed to leave because of "civilian pressure" resulting from intense airstrikes and "warplanes that do not leave the sky," adding that Harasta residents have spent the last three months in shelters.
But the arrangement leaves other fighters for the Failaq al-Rahman group still inside. They government is threatening to move on them if they do not also agree to depart.
In violence elsewhere, an airstrike on a market in the village of Harem in northwestern Syria killed at least 28 people, according to observers and the opposition's Civil Defense group.
The Syrian Observatory for Human Rights said the dead included 11 children and women, and the overall death toll could still rise since many others were critically wounded.
The Syrian Civil Defense, also known as White Helmets, said the airstrike killed 37, mostly women or children.
Harem is in Idlib province, which is mostly controlled by rebels and has been subjected to intense airstrikes recently.
- AP