BEIRUT — Syrian government warplanes bombarded rebel-held areas around the country Saturday while insurgents shelled government-held neighborhoods in violence that left dozens killed or wounded hours after a new U.S.-Russia agreement was reached to try and reduce violence in the war-torn country.

The United States and Russia announced a deal that foresees a nationwide cease-fire starting on Monday, followed a week later by an unexpected new military partnership targeting Islamic State and al-Qaida militants as well as the establishment of new limits on President Bashar Assad’s forces.

State news agency SANA said the Syrian government accepts the agreement, adding that hostilities will stop in the northern city of Aleppo, the country’s largest, for “humanitarian reasons.” It did not say when the violence will stop, adding that the U.S.-Russia agreement “was reached with the knowledge and approval of the Syrian government.”

The violence shows that it might be difficult to implement the U.S.-Russia agreement as both countries enjoy limited influence on the government and insurgent groups to cease the bombardment.

A cease-fire reached by the two world powers earlier this year and put into effect in late February failed shortly afterward and was followed by months of violence the killed thousands.

Russia is a main backer of Assad’s government while the U.S. has been supporting rebel groups trying to remove him from power. Syria’s conflict, now in its sixth year, has continued despite several rounds of peace talks and international attempts to try end the violence. At least a quarter million people have been killed and half the country’s prewar population displaced.

The air raids were mostly in the northern provinces of Idlib and Aleppo. Aleppo has been the center of violence in Syria in recent months where some 2,200 people, including some 700 civilians, have been killed since last July according to the Britain-based Syrian Observatory for Human Rights, which tracks violence in Syria. .

The Observatory and the Local Coordination Committees also reported an airstrike in the Damascus suburb of Douma where the dead included four children.

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