UPDATE 1-Bomb kills 8 in Syrian city of Raqqa

A bomb attack in the Syrian city of Raqqa killed eight people on Tuesday, including four members of the U.S.-backed Syrian Democratic Forces, a security source in northern Syria said.

The blast also killed four civilians and wounded three members of the Kurdish-led internal security forces known as the Asayish, the source said. Witnesses said people including SDF members gathered at the scene after the first blast, which was followed by a bigger explosion that caused the casualties.

"I heard the sound of a big explosion and people were rushing and I saw people blown up with body parts," an injured witness who was rushed to hospital told Reuters. There has been an steady increase in attacks on areas controlled by the Syrian Democratic Forces, mainly east of the Euphrates River.

The group, which is led by the Kurdish YPG militia, has warned that Islamic State militants will intensify their insurgent activities after being defeated defeat in their last enclave in Syria last month. (Writing by Suleiman Al-Khalidi Editing by Tom Perry and Giles Elgood)

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