Heavy air strikes hit parts of Aleppo on Thursday after the Russian-backed Syrian army announced an offensive to take full control of the largest city in the country.

The announcement came as world leaders failed in their attempt to resurrect a ceasefire, which after a US-led coalition air strike on a Syrian army post seems to have collapsed. A UN aid convoy was also hit shortly after the ceasefire was ended. Washington blames the attack on Russia - a claim Moscow denies.

So with more than 400,000 people killed since the conflict began five years ago and millions having fled, is there any hope for Syria?

In this week's Headliner, we speak to Staffan de Mistura, UN special envoy for Syria, about his ongoing efforts to find a solution to the war.

"As far as I'm concerned, this is considered the worst humanitarian tragedy since World War II", de Mistura says.

On the complexity of finding a diplomatic solution to the conflict, the special envoy tells Mehdi Hasan, "I've never seen so many players with so many different agendas."

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Source: Al Jazeera News