What's behind Russian humanitarian corridors in Aleppo?

Humanitarian passages out of the northern Syrian city of Aleppo are causing controversy.

More than 150 families and some opposition fighters have left the rebel-held areas of the northern Syrian city of Aleppo.

Government and Russian forces say they've opened humanitarian corridors to allow people to leave the besieged city.

But activists have expressed doubts over the plan, saying it's likely a pretext for the government to launch an attack and gain full control of Aleppo.

And the UN envoy to Syria has also questioned Russia's involvement, saying safe passages are the work of the United Nations.