Syria's President Bashar al-Assad told a Swiss TV station that government forces had to rid the city of Aleppo of rebel "terrorists" under its constitutional mandate to protect the civilian population.

"That's our mission, according to the constitution, according to the law, that we have to protect people, that we have to get rid of those terrorists from Aleppo. This is where we can protect the civilians," he said in an interview with Swiss broadcaster SRF conducted on Tuesday and posted on SRF's website on Wednesday.

"How can you protect them while they are under the control of terrorists? They've been killed by them, and they've been controlled fully by the terrorists. Is it our role to sit aside and watch if that's how we can protect the Syrian people? We need to attack the terrorists, that's self-evident."