This April 30, 2017 photo provided by the Syria Democratic Forces (SDF), shows a fighter from the SDF carrying weapons as he looks toward the northern town of Tabqa, Syria. U.S.-backed Syrian forces say the battle for control of the Islamic State group's de facto capital Raqqa, in northern Syria, will begin "within days." (Syrian Democratic Forces, via AP, File)
A U.S.-backed Syrian force said Tuesday it has begun an offensive to capture the northern city of Raqqa, the de facto capital of the Islamic State group, after months of clearing operations.
Raqqa was among the first cities captured by IS, in January 2014, and has been the home of some of the group's most prominent leaders, including those who planned the November 2015 Paris attacks and other international assaults.
The battle for the city is expected to be long and bloody, and could mark a major turning point in the war against the extremists.
Talal Sillo, a spokesman for the Kurdish-led Syrian Democratic Forces, told reporters that operations have begun in coordination with the U.S.-led coalition.
"We declare today the beginning of the great battle to liberate the city of Raqqa, the alleged capital of terrorism and terrorists," Sillo told a news conference held in northern Syria. "Morale is high and military readiness to implement the military plan is complete, in coordination with the U.S.-led coalition."
SDF fighters began advancing toward Raqqa in November, capturing wide areas of northern Syria from the extremists. Last week, they reached the northern and eastern gates of the city after intense clashes under the cover of U.S.-led airstrikes.
Raqqa is currently surrounded from the east, north and west, and opposition activists have reported intense shelling and airstrikes on the city since Monday night, which killed at least 12 people.
The extremists are not expected to give up easily. Iraqi forces launched an offensive to capture the northern city of Mosul, the largest held by IS, in October, and heavy fighting is still underway there.
IS stormed across large areas in Syria and Iraq in 2014, declaring a self-styled Islamic caliphate.
But it has lost much of that territory over the past two years following grueling campaigns by an array of Syrian and Iraqi forces. The fighting has devastated communities in both countries and forced hundreds of thousands of people to flee their homes.
IS has been fortifying its positions in Raqqa for months, setting up barriers and hanging sheets of cloth over main streets to provide cover from warplanes.
A belt of land mines and militant checkpoints circle the city. Inside, all the men have been ordered to wear the jihadis' garb of baggy pants and long shirts in order to make it more difficult to distinguish militants from civilians.
Sillo called upon Raqqa residents to stay away from "the enemy's centers and points of fighting."
The Britain-based Syrian Observatory for Human Rights reported heavy clashes on the edge of Raqqa's eastern neighborhood of Mashlab as well as inside Division 13, a former Syrian army base now controlled by IS north of the city.
Earlier Tuesday, state news agency SANA reported that the airstrikes by the U.S.-led coalition killed 12, including women and children. It said the families were fleeing the city in boats across the Euphrates River ahead of an expected all-out attack by the SDF.
The Observatory said 21 people were killed in the Monday night airstrikes. It said they were likely carried out by the U.S.-led coalition.