Battle for ISIL's Syrian headquarters is huge test for U.S.-backed forces

WASHINGTON — A critical offensive to retake the Islamic State’s remaining stronghold in Syria depends on a loosely organized and lightly armed U.S.-backed force to breach the militants' heavily defended city.

Despite the challenge in capturing Raqqa, the Syrian Democratic Forces (SDF) have shown a remarkable willingness to fight and can point to a string of successes in driving militants from towns throughout northern Syria, said Col. John Dorrian, a U.S. military spokesman in Baghdad. “They’ve been successful in defeating (the Islamic State) anywhere they’ve encountered them,” he said.

The Islamic State “considers Raqqa their capital in Syria, so we expect resistance to stiffen as forces move closer to the city,” Dorrian said.

The Raqqa offensive, which started earlier this month, will be the SDF's largest test.

President-elect Donald Trump has expressed skepticism about a separate covert U.S. program to support opposition groups fighting to overthrow Syrian President Bashar Assad, who has so far survived after more than five years of civil war. Trump has not commented on the Pentagon program that supports the SDF's fight against the Islamic State.

The SDF is about 30,000 strong and consists mainly of Kurds. Turkey's government opposes the force because of a push by Kurds in Turkey, Syria and Iraq to carve out an independent state, which could be enhanced by victories over the Islamic militants.

Partly to allay Turkey’s concern, the United States has given $30 million in weapons and other equipment only to the non-Kurdish faction of the SDF.

The Pentagon is trying to increase Arabs in the force because Raqqa is an Arab city, and a mostly Kurdish invasion would likely alienate residents.

The U.S. military had urged the group to advance on Raqqa at the same time Iraqi forces are attacking Mosul, Iraq’s second-largest city, to regain control from the Islamic State. The thinking is that simultaneous operations will pose a tougher challenge for the militants.

The Pentagon has several hundred advisers in Syria working with the SDF and has supported the ground campaign with airstrikes.

The SDF is stitched together from hundreds of tribal groups and lacks an organized command structure. The Pentagon said only a fraction of the 30,000 fighters are involved in the Raqqa campaign.

The Syrian Defense Forces are attempting to isolate Raqqa by cutting off supply routes into the city before entering it. “We do expect this isolation phase to go on for a number of weeks, perhaps months even,” Dorrian said.

The Kurds have proven to be fierce and tenacious fighters. Months after Iraq's military collapsed in the face of the Islamic State's 2014 invasion, a small group of Kurds managed to hold off a massive assault by the militants on the Syrian city Kobani, which is on the Turkish border. They dealt one of the first blows to the Islamic State, proving their fighting skills.

More recently, a force of Kurds and Arabs drove the Islamic State from the town of Manbij, another major defeat for the Islamic State. The SDF has retaken about 100 square miles of terrain since the Raqqa operation began, the U.S.-led coalition said.

U.S. military officials said the Manbij operation was a model for Arab-Kurdish cooperation in defeating the Islamic State: Arab forces participated in the offensive and are responsible for holding the mostly Arab city.

U.S. officials said they will pursue a similar strategy in Raqqa. "We're going to try to recruit and train a force that's from the local area," said Lt. Gen. Stephen Townsend, commander of the task force for Iraq and Syria.

The Pentagon said U.S.-led coalition aircraft have dropped 250 munitions, including bombs and rockets, since the Raqqa operation began. That kind of support is critical to the success of the operation, said Andrew Tabler, an analyst at the Washington Institute for Near East Policy.  “If we provide support it will hold together.”