SDF fighters began advancing towards Raqqa in November and last week reached the northern and eastern gates of the city.
US-backed Syrian forces have begun an offensive to capture the northern city of Raqqa, the de facto capital of the Islamic State group.
Talal Sillo, a spokesman for the Kurdish-led Syrian Democratic Forces (SDF) , said on Tuesday that operations have begun in co-ordination with the US-led coalition.
SDF fighters began advancing towards Raqqa in November, capturing wide areas from the extremists. Last week, they reached the northern and eastern gates of the city.
Raqqa is currently surrounded from the east, north and west, and opposition activists have reported intense shelling on the city since Monday night, which killed at least 12 people.
State news agency Sana reported that women and children were among the dead after the strikes by the US-led coalition. It said the families were fleeing the city in boats across the Euphrates River ahead of the expected all-out attack by the SDF.
The battle is likely to be long and bloody, and the extremists are not expected to give up easily.
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.
Talal Sillo, a spokesman for the SDF, said: “We declare today the beginning of the great battle to liberate the city of Raqqa, the alleged capital of terrorism and terrorists.
“Morale is high and military readiness to implement the military plan is complete, in co-ordination with the US-led coalition.”
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 war planes.
A belt of landmines 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.
A US military official said the fight in Raqqa “will be long and difficult”.
But Lt Gen Steve Townsend, the top US commander in Iraq, said the offensive will deliver a decisive blow to the idea of IS “as a physical caliphate”.
As the operation begins to take Raqqa, Iraqi forces have already captured much of Mosul, the largest city in that country held by the extremist group.
