Tens of thousands of Syrians have fled a government offensive on rebel-held areas south of the city of Aleppo in the past three days, an activist says, according to BBC News.

Dr Zaidoun al-Zoabi, head of the Union of Syrian Medical Relief Organisations, told the BBC that several villages he had visited were empty. He saw thousands of people on the move, with no shelter or medical support.

The government offensive is the latest of at least four launched with Russian air support in the past two weeks.

Aside from the Aleppo countryside, they are taking place in mostly rural areas north of the cities of Homs and Hama, and in the north of the coastal province of Latakia.

Rebel fighters - not including jihadist militants from Islamic State (IS) - had penetrated most of these strategically important areas earlier this year.

Their gains prompted Russia to launch an air campaign to bolster President Bashar al-Assad in September, and also reportedly led Iran to deploy hundreds of combat troops. Tehran has previously only acknowledged sending military advisers.