The United States, France and Britain said they would provide air support for the offensive, which was announced at a news conference in Ein Issa, north of Raqqa, by a coalition of Kurds and Arabs known as the Syria Democratic Forces.

But it lacked details on how the group dominated by Kurds plans to oust the militants from the city, home to nearly 200,000 mostly Sunni Arabs and an estimated 5,000 ISIS terrorists.

Unlike several successful military efforts to drive ISIS terrorists out of cities in Iraq, the Raqqa offensive faces several political obstacles and is likely to be much more complex.

In Iraq, a US-led coalition is working with the government in Baghdad, but Washington and its partners in Syria are relying on a hodgepodge of local Arab and Kurdish opposition groups, some of which are fierce rivals.

The tensions are exacerbated by Turkish forces.

Still, the start of the Raqqa offensive, which aims initially at isolating and encircling the city, increases the pressure on the ISIS, making it harder for its fighters to move reinforcements between Syria and Iraq.

The city, which has been under ISIS (ISIL, IS, Daesh) control since early 2014, is home to some of the group's top leaders and is seen as the key to defeating the group militarily.

SA - 12