Syrian Democratic Forces (SDF) fighters shoot a drone they said belonged to Islamic State fighters on the bank of the Euphrates river, west of Raqqa city Thomson Reuters

The long-awaited offensive by U.S.-backed Syrian forces to liberate the self-proclaimed Islamic State capital of Raqqa, Syria, will begin in days, Pentagon officials told the Washington Examiner Thursday.

"The sh-- is about to go down in Raqqa," one official said, speaking under condition of anonymity. "I would expect to see the assault begin in the coming days."

While the Pentagon is not saying publicly when the offensive will kick off, it has acknowledged that all the forces are in place, small arms are being handed out to the Syrian Democratic Forces, and civilians have been told to get out of Raqqa so they are not caught in the crossfire.

"The SDF is poised around Raqqa. They are within 3 kilometers [1.8 miles] from the north and the east, and are about 10 kilometers [6 miles] from the city to the west," said Col. Ryan Dillon, a U.S. military spokesman in Baghdad.

"The Syrian Democratic Forces have given instructions to the citizens of Raqqa to vacate," Dillion told reporters at the Pentagon, noting that so far almost 200,000 people have left the city for nearby refugee camps and settlements.

The U.S. has also begun distributing small arms and ammunition to the Syrian fighters, but has not yet provided anti-tank weapons, an indication that the planned offensive, while coming soon, is not imminent.

Dillon said the distribution of weaponry will be carefully inventoried and limited to what is needed for specific combat objectives, and that a list of what was provided to the Syrian fighters will be shared with Turkey, a NATO ally that is upset that the U.S. is providing arms to some Kurdish elements it considers terrorists.

The U.S.-led coalition has also stepped up airstrikes in recent days, conducting nearly 60 strikes targeting ISIS fighting positions, construction equipment, artillery systems, and command and control nodes, Dillon said.

The beginning of the Raqqa offensive comes as the operation to liberate the Iraqi city of Mosul is drawing to a close.

Fewer than 1,000 ISIS fighters are left in west Mosul, where they hold about six square miles, but are surrounded in three neighborhoods in the old city section with no escape.

But 80,000 to 150,000 civilians are also trapped in the densely populated city center, as Iraqi forces prepare for what is expected to be some of the most ferocious urban combat of the campaign.

Those Mosul residents have been told not to drive cars or motorcycles so they won't be mistaken for vehicle bombers, the weapon of choice of ISIS.