Syria 'worst humanitarian disaster in yrs'

The ongoing Syrian conflict represents one of the worst humanitarian disasters the world has seen in years, Foreign Minister Julie Bishop says.

There are reports of mass civilian casualties in the city of Aleppo and humanitarian assistance is desperately required.

"This is one of the worst humanitarian disasters that we have witnessed in many, many years," she told Sky News on Wednesday.

Ms Bishop said Australia has been calling for a ceasefire and for humanitarian corridors to be set up so civilians can leave and aid get through.

The conflict has been beset with claims and counter-claims, which she witnessed first hand during international meetings.

"Russia and the United States must find a way forward to stop the killing and to allow humanitarian relief to be provided to the suffering people of Aleppo," she told ABC radio.

The minister again reiterated the need for a political solution.

"To say that (President) Assad must go, I'm afraid that moment passed a long time ago."

Reports of executions in Aleppo must be investigated, Ms Bishop said.