Syrian government forces and their allies took control of a strategic crossroads in Raqqa province on Friday in their latest advance towards Islamic State strongholds in the area, the army and a monitoring group said. The seizure of the junction, which leads to Raqqa city, Islamic State's de facto capital and also to Tabqa, another city it controls, came as part of a week-old Syrian government offensive against the jihadists, backed by Russian air power. The British-based Syrian Observatory for Human Rights monitoring group said government-allied forces were 15 km (9 miles) from Tabqa. Both the Observatory and the army said large numbers of IS fighters had been killed in the campaign.