Syrian President Bashar al-Assad has offered an amnesty to armed rebels battling his forces if they surrender, the official SANA news agency has reported.

Key points: Rebels who lay down weapons or release hostages will be given amnesty, official news agency says

Rebels who lay down weapons or release hostages will be given amnesty, official news agency says Russia says it has launched a large scale operation to open humanitarian corridors to Aleppo

Russia says it has launched a large scale operation to open humanitarian corridors to Aleppo The UN's envoy on Syria says he hopes peace talks can resume at the end of August

"Everyone carrying arms... and sought by justice... is excluded from full punishment if they hand themselves in and lay down their weapons," SANA said, quoting a presidential decree on the three-month amnesty offer.

The reprieve also includes any rebel who frees a hostage, according to the decree text.

The offer comes as opposition neighbourhoods of Aleppo city are effectively surrounded by pro-government forces, sparking fears for the more than 200,000 people trapped there.

Mr Assad's ally Russia said it had launched a "large-scale" operation with the Syrian Government to open humanitarian corridors for civilians and fighters fleeing the northern city.

Pro-government forces effectively surround opposition neighbourhoods of the divided city, sparking fears for at least 200,000 people trapped there.

Residents have reported food shortages and spiralling prices in rebel districts since regime forces cut off the opposition's main supply route into the city earlier this month.

Defence Minister Sergei Shoigu told Russian news agencies that three humanitarian corridors were being opened to "aid civilians held hostage by terrorists and for fighters wishing to lay down their arms" and one more corridor to the north of the city for rebels to flee with their weapons.

An injured child is carried away from the scene of shelling in the rebel-held Syrian town of Aleppo. ( Supplied: Syrian American Medical Society )

Medical posts and food handouts would be provided along the routes intended for civilians and fighters who surrender, Mr Shoigu said.

Mr Assad has issued several amnesties in recent years, including one in July 2015 for people who have dodged service or defected from the army.

The UN's Syria envoy Staffan de Mistura said this week he hoped peace talks aimed at ending more than five years of brutal conflict could resume at the end of August.

More than 280,000 people have been killed in Syria since the war began in March 2011 with anti-government protests that were met with a brutal regime crackdown.

AFP