(AFP) -- The drive for the northern city at the heart of ISIS' Syrian territory has been seven months in the making and has been backed US-led coalition air support, military advisers and weapons deliveries.

On Tuesday, Arab and Kurdish SDF fighters advanced to the city's eastern edge and broke into Raqqa for the first time.

"Our forces entered the city of Raqqa from the eastern district of Al-Meshleb," SDF commander Rojda Felat told AFP.

"They are fighting street battles inside Raqqa now, and we have experience in urban warfare," she said.

Fierce clashes were also raging on the northern outskirts of the city, which lies on the winding Euphrates River, Felat added.

The Syrian Observatory for Human Rights said the SDF had seized a number of positions inside Raqqa.

"They have taken control of a checkpoint in Al-Meshleb, as well as a number of buildings," Observatory head Rami Abdel Rahman said.

"The advance came after heavy air strikes by the US-led coalition," he told AFP.

- 'Great battle' begins -

After months sealing off access routes to the city from the east, north and west, the SDF on Tuesday announced a new phase in their fight for Raqqa.

"We declare today the start of the great battle to liberate the city of Raqqa, the so-called capital of terrorism and terrorists," SDF spokesman Talal Sello told reporters in the village of Hazima, north of the city.