The U.S-backed Syrian Democratic Forces (SDF) are on the verge of seizing full control of the southern neighborhoods of Raqqa held by Islamic State (IS) militants, a Kurdish official said on Tuesday. The U.S.-led coalition said SDF fighters advancing from the east were within 300 metres (330 yards) of meeting up with those advancing from the west. The SDF was making "consistent gains" every day, the coalition spokesman said. The SDF launched its U.S.-backed campaign to seize Raqqa in early June. The assault on IS de facto capital in Syria overlapped with the campaign to drive IS from the Iraqi city of Mosul, where IS was defeated last month. The Kurdish official told Reuters SDF fighters advancing from the east and the west remain separated by a few streets where fighting continued. Full control of the southern districts would sever IS last remaining path to the Euphrates River which is to the south of the city. "There is a fierce resistance from Daesh, so we can't determine when exactly we'll take (full control)," said the official, referring to IS. "Around 90 percent of the southern neighborhoods are liberated," the official added. The spokesman for the U.S.-led coalition said SDF fighters had also captured around 10 square km (4 sq miles) of territory from IS north of Raqqa in the last two days. "We've seen a less coherent ISIS defense in Raqqa compared to Mosul. ISIS is still using car bombs, booby traps, and civilians to hide behind, but their inability to address the multiple advances from the SDF is apparent," coalition spokesman Col. Ryan Dillon said in response to emailed questions from Reuters. The SDF is dominated by the Kurdish YPG militia, and is the main partner for the U.S.-led coalition against IS in Syria. Last week, the Syrian Observatory for Human Rights reported that the SDF has captured half of Raqqa. IS has lost large expanses of territory in Syria over the last year to separate campaigns waged by the SDF, the Russian-backed Syrian military, and Turkey-backed Syrian rebels.