US-backed Syrian forces say they are close to capturing an Islamic State-held town that lies halfway between the former IS-stronghold of Tabqa and its de facto capital, Raqqa, in northern Syria.

The Kurdish-led Syrian Democratic Forces say they are in control of 90 percent of the town of Mansoura, approximately 26 kilometers (16 miles) southwest of Raqqa.

The Britain-based Syrian Observatory for Human Rights says the SDF has been engaged in fierce fighting with IS militants along the southern bank of the Euphrates River, around Mansoura. The river leads to Raqqa.

The US has backed the SDF with weapons, airpower, and ground support in its campaign to defeat the Islamic State group in Syria. Its target for now is Raqqa, which has been held by the militants since 2014.