The rebels have set their sights on an area where President Bashar al-Assad’s government has long maintained strength.

The leader of Syria’s most powerful insurgent group has toured the seized city of Aleppo in a surprise visit, for the first time since the group captured large parts of the city last weekend, as fierce fighting intensifies in the government-led counter-offensive in northern Hama.

Islamist rebels have been advancing through large swathes of the country's north-west in the past week, threatening the rule of Syria's long-time president, Bashar Al-Assad.