BEIRUT (AP) — The Latest on the Syrian conflict (all times local):

3:15 p.m.

Syrian activists say a rocket or mortar barrage struck a preschool in an opposition-controlled suburb of the capital, Damascus, killing at least six children.

The activist-run Unified Medical Bureau of Eastern Ghouta reported the death toll and said medical facilities in the suburb of Harista received tens of wounded children and adults following Sunday's shelling.

The locally-run Education Directorate said government forces struck the school during the first recess of the day. It said more than 25 children were wounded in addition to the six killed.

The Britain-based Syrian Observatory for Human Rights, which relies on a network of local activists, also blamed government forces for the strike.

1 p.m.

U.S.-backed Kurdish-led Syrian forces have announced the start of a campaign to retake the Islamic State's de facto capital of Raqqa from the extremist group.

The announcement by the Syria Democratic Forces was made Sunday at a press conference in Ein Issa, north of Raqqa.

It comes more than two weeks after U.S.-backed Iraqi forces began a campaign to clear IS militants from their stronghold in Mosul, Iraq.

The SDF is dominated by the main Syrian Kurdish fighting force known as the People's Protection Units, or YPG.

The United States considers the Syrian Kurdish fighters as the most effective force against the IS, but Turkey views them as a terror organization and has said it will not accept a role for the Kurds in the liberation of Raqqa.