US-backed Syrian alliance declares attack on Islamic State in Raqqa

The new offensive ratchets up pressure on Islamic State at a critical moment, with its fighters already battling an assault by Iraqi security forces on their remaining Iraqi stronghold in the northern city of Mosul.

A statement issued by the U.S.-backed Syria Democratic Forces (SDF), an alliance of Kurdish and Arab armed groups, said the long anticipated campaign, called Euphrates Anger, started late on November 6.

"The general command of the Syria Democratic Forces announces the blessed start of its major military campaign to liberate the city of Raqqa," Jehan Sheikh Amad, an SDF spokeswoman, told a news conference in the Syrian town of Ain Issa, 50 km (30 miles) north of Raqqa.

The United States would be coordinating air strikes with the SDF, which includes the powerful Kurdish YPG militia and has been the main partner on the ground in Syria for the U.S.-led coalition against Islamic State.

Raqqa is the Syrian bastion of the ultra-hardline Sunni Muslim Islamic State, from where it runs training camps and directs operations. The group has been overseeing civilian life in the city including bakeries, banks, schools and mosques.

Brett McGurk, U.S. President Barack Obama's counter-Islamic State envoy, told reporters during a stopover in Amman that the "initial phase" of the Raqqa offensive had begun.

"The Raqqa campaign will proceed in phases, deliberate phases, there is an isolation phase which began today and subsequent phases to ensure we kick out Daesh out of Raqqa," McGurk said.

The SDF statement said the operation aimed to "isolate and then topple the capital of international terrorism", indicating an initial phase aimed to surround Raqqa before any move to seize it. No timeframe was given.