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By The Associated Press

The Islamic State on Sunday repelled an advance by U.S.-backed forces on one of its main bastions in northern Syria, seizing back territory it had previously lost, Syrian activists and the extremist group said.

The group said its fighters infiltrated villages and mountains near the ISIS-held town of Manbij that were seized last month by the Syrian Democratic Forces, a Kurdish-dominated group aided by U.S. special forces that also includes Arab fighters.

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In a statement carried by the ISIS-run Aamaq news agency, the group said a fighter driving a car packed with explosives struck a gathering of Kurds amid clashes in the northwestern part of Manbij.

Manbij, which lies on a key supply line from Turkey to the group's de facto capital of Raqqa, has been encircled by the SDF for weeks. Heavy clashes were taking place inside.

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The Syrian Observatory for Human Rights also reported the ISIS counteroffensive. The Britain-based group, which relies on a network of activists on the ground, reported heavy clashes accompanied by U.S.-led airstrikes and a series of explosions that shook the town, which it attributed to ISIS suicide operations.

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