Syrian government warplanes carried out several airstrikes in the Eastern Ghouta area east of Damascus on Sunday, a day after the Syrian military declared a cessation of hostilities in the area, the Syrian Observatory for Human Rights said.
The British-based monitoring group said Saturday had been relatively calm after the cease-fire took effect with isolated incidents of shellfire.
On Sunday, six airstrikes hit the towns of Douma and Ain Terma in rebel-held Eastern Ghouta, it reported.
There was no immediate comment from the government or army.
Syria's military declared a "cessation of fighting activities" starting at noon on Saturday in besieged Eastern Ghouta, which has long been controlled by the opposition.
One rebel group in Eastern Ghouta quickly welcomed the cease-fire.
A separate statement from Cairo-based political opposition movement Al-Ghad, headed by Ahmad Jarba, said the agreement had been reached in Cairo, sponsored by Egypt and Russia and with the involvement of mainstream rebel groups.
There was to be a full cease-fire in Eastern Ghouta, no government forces would enter the area and aid would be allowed in, it said.
Numerous attempts at a lasting cease-fire in western Syria, where rebels have lost ground to government forces and their allies over the last year, have often collapsed with both sides trading the blame.
The United States, Russia and Jordan reached a cease-fire and "de-escalation agreement" for southwestern Syria this month, which has reduced violence. That agreement did not include Eastern Ghouta.
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