The watchdog said an additional 2,500 people, among them fighters, will also leave Eastern Ghouta overnight.
"A total of 5,000 people, among them 1,500 fighters, will leave Eastern Ghouta between tonight and dawn," the head of the Observatory, Rami Abdel Rahman, told dpa.
State news agency SANA reported that the some 100 buses would leave Eastern Ghouta late Friday.
The group was evacuated from the areas of Arbeen, Zamlka, Ain Turma and Jouber, located in Eastern Ghouta's south-western sector that was controlled by the rebel group Faylaq al-Rahman, the watchdog said.
Evacuations conducted over the past week have allowed Syrian President Bashar al-Assad's troops to strengthen their hold on Eastern Ghouta, the target of severe bombardments in recent weeks.
The Observatory said that so far some 107,000 people have left Eastern Ghouta towards regime-controlled areas, while some 42,000 have headed to Idlib.
The enclave's town of Douma remains the only pocket under rebel control. Douma's population is now estimated to be 200,000.
The Syrian government had earlier given the rebel group Jaish al-Islam in Douma 72 hours to leave the area, Syrian television and radio reported on Friday.
According to the broadcasters, the 72-hour deadline had started on Wednesday night. The group has been in talks with Russian mediators for the past few days.
Russia's Defence Ministry on Friday said it had brokered a deal that would see rebels abandon Douma, but Jaish al-Islam quickly denied it.
The head of the group's political department, Mohammed Alloush, told the Dubai-based Al Arabiya television that the deadline "is a mere propaganda stunt by the Syrian regime to try to gain more from the ongoing negotiations with the Russians."
Alloush told dpa on Thursday: "We are negotiating to stay or find a compromise. We do not want to leave our land. We are the sons of the country and the people of the region. We are there before any Russian or Iranian intervention."
He reiterated his group's refusal to accept any forced displacement to north-western Idlib, which is controlled by the al-Qaeda-linked group Hayat Tahrir al-Sham.
The full recapture of Eastern Ghouta will mark the biggest victory for al-Assad since December 2016, when his forces regained complete control of the northern city of Aleppo from the opposition following a Russian-backed offensive.
------------------------------------------------------------------------------------------------------------------------
"A total of 5,000 people, among them 1,500 fighters, will leave Eastern Ghouta between tonight and dawn," the head of the Observatory, Rami Abdel Rahman, told dpa.
State news agency SANA reported that the some 100 buses would leave Eastern Ghouta late Friday.
The group was evacuated from the areas of Arbeen, Zamlka, Ain Turma and Jouber, located in Eastern Ghouta's south-western sector that was controlled by the rebel group Faylaq al-Rahman, the watchdog said.
Evacuations conducted over the past week have allowed Syrian President Bashar al-Assad's troops to strengthen their hold on Eastern Ghouta, the target of severe bombardments in recent weeks.
The Observatory said that so far some 107,000 people have left Eastern Ghouta towards regime-controlled areas, while some 42,000 have headed to Idlib.
The enclave's town of Douma remains the only pocket under rebel control. Douma's population is now estimated to be 200,000.
The Syrian government had earlier given the rebel group Jaish al-Islam in Douma 72 hours to leave the area, Syrian television and radio reported on Friday.
According to the broadcasters, the 72-hour deadline had started on Wednesday night. The group has been in talks with Russian mediators for the past few days.
Russia's Defence Ministry on Friday said it had brokered a deal that would see rebels abandon Douma, but Jaish al-Islam quickly denied it.
The head of the group's political department, Mohammed Alloush, told the Dubai-based Al Arabiya television that the deadline "is a mere propaganda stunt by the Syrian regime to try to gain more from the ongoing negotiations with the Russians."
Alloush told dpa on Thursday: "We are negotiating to stay or find a compromise. We do not want to leave our land. We are the sons of the country and the people of the region. We are there before any Russian or Iranian intervention."
He reiterated his group's refusal to accept any forced displacement to north-western Idlib, which is controlled by the al-Qaeda-linked group Hayat Tahrir al-Sham.
The full recapture of Eastern Ghouta will mark the biggest victory for al-Assad since December 2016, when his forces regained complete control of the northern city of Aleppo from the opposition following a Russian-backed offensive.
------------------------------------------------------------------------------------------------------------------------