As the West focuses on defeating the Islamic State in Syria, another jihadist group has taken over swathes of territory in the country and is threatening to establish another radical mini-state, the Mail Online reports.

The Al-Qaeda-backed Nusra Front has been gaining control of Idlib province in north-west Syria since November, driving out other rebel groups, including western-armed moderates.

In the past two weeks, it has begun to extend its control into the country's largest city, Aleppo, which is regarded as one of the last areas in northern Syria with a significant presence of moderate rebel groups.

"Nusra are trying to do in Aleppo what they did in Idlib. They want to wipe out the (Western-backed) Free Syrian Army," said Mazen Alhor, an opposition activist in the city.

"They are starting to behave like ISIS — kidnapping, enforcing Islamic rules. They have a strategy, they want an Islamic state."

Sami Mashaal, the head of the Shura Council for the Revolution in Aleppo, said that the Nusra Front had begun establishing checkpoints inside the city last week. "They are harassing people, trying to enforce Islamic rules — and civilians are getting angry about it," he said.

The Nusra Front was established in 2012 by Abu Muhammad al-Julani, a Syrian al-Qaeda commander. It was originally allied to the extremist group that eventually morphed into Islamic State.

However, the two groups turned against each other at the start of last year, in a war-inside-a-war that has cost thousands of lives.