Islamic State militants have pushed back Kurdish-led forces attempting to take control of the city of Manbij. The terrorist group is staging a counteroffensive to stop US-backed troops from cutting off their key access route to Turkey.

The Syria Democratic Forces (SDF), which is made up of Arab and Kurdish fighters, have been involved in a bloody month-long battle in Manbij to secure the Syrian-Turkish borders.

Suicide bombers blew up a vehicle packed with explosives, according to the Syrian Observatory for Human Rights. The British-based organisation confirmed that Islamic State (Isis) had evicted SDF fighters from one of the main districts in the south of the city, which was the scene of fierce conflict.

Isis (IS) militants are also reported to have retaken a village to the north-west of the city, according to EKurd Daily.

This was denied by an SDF spokesman, who refuted claims that US-led coalition troops had withdrawn from key positions in the city. "I stress that we have not retreated any step and all our positions are under our control," Sharfan Darwish, spokesman for the SDF-allied Manbij Military Council, said in a statement.

He added that they would press on with the campaign until they "liberated Manbij". The alliance now plans to advance on the IS stronghold of Raqqa, once the northwestern city of Manbij is taken back from the Islamist militants, according to Brett McGurk, special envoy to the anti-Isis coalition war.

"The Manbij operation, it's ongoing on right now, it's hard fighting, once that is done, that sets the conditions for Raqqa," McGurk told the US Senate Foreign Relations Committee hearing.

However, the advance on Manbij is painfully slow, as IS fighters have snipers in key positions, planting mines and preventing civilians from leaving. US aircraft are unable to bomb the city for fear of inflicting major casualties on the civilian population, according to Kurdish sources.

Manbij is of strategic importance to IS, serving as a channel bringing in foreign members and provisions from the Turkish border.