"We would then say anywhere between 80,000 to 150,000 are in the Douma area still under control of the armed opposition groups, Jaish al-Islam the biggest", Egeland said. The United States helped Kurdish-led forces drive IS from much of northern and eastern Syria, and has hundreds of troops embedded with them.
The airstrikes came as negotiations are underway between local councils of the main towns in eastern Qalamoun, and representatives from the Syrian government and the Russian Reconciliation Center in Syria.
The Syrian Observatory for Human Rights, a Britain-based Syrian war monitor, said that Jaish Al Islam and the Syrian government agreed on a settlement to secure those who wish to stay in Douma, allow the evacuation of those who want to leave, surrender heavy artillery to the Syrian regime and allow police to be deployed in the city.
The last Syrian rebel group in eastern Ghouta near Damascus began withdrawing on Monday under an agreement with the government, state media said, though a military source said a group of insurgents were still rejecting the deal.
If confirmed, the departure of Jaish al-Islam from Douma would mark the end of the war for eastern Ghouta, wiping out an opposition stronghold near Damascus and underlining President Bashar al-Assad's unassailable position in the war.
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A rebel faction trapped by government forces outside the Syrian capital agreed to evacuate to northern Syria on Sunday as reports swirled of a larger agreement that would have the government retake full control of the eastern Ghouta region after seven years of revolt. There was no comment from the Army of Islam. More than 40,000 rebels and their family members have chosen to relocate, according to the Russian military. More than 120,000 people fled their homes under the five-week assault, seeking safety behind government lines, according to the Russian military. The source said on Tuesday the government had set a deadline for militants to leave Douma, without saying how long.
Ahmad Ramadan, a prominent opposition figure in exile, told the Saudi TV channel al-Arabiya that the Army of Islam was still engaged in talks with Russian Federation over the future of the town.
Bilal Abu Salah, a media activist in Douma, said Tuesday that the convoy of buses entering Jarablus contained humanitarian cases, including injured members of Jaish al-Islam.
Turkey, with the support of allied Syrian opposition forces, is carrying out its own military operations in northern Syria, against a USA -allied Kurdish militia. Ahmad Ramadan, an opposition figure, revealed on Sunday that Turkey was party to the talks as well.