Russian and Syrian jets struck the rebel-held city of Idlib on Sunday in the second day of intensive bombing in northern Syria aimed at pushing back insurgents who had swept through to the city of Aleppo,

The Syrian army said on Saturday dozens of its soldiers had been killed in a major attack led by Islamist Hayat Tahrir al-Sham rebels who swept into the city of Aleppo, forcing the army to redeploy in the biggest challenge to President Bashar al-Assad in years.

The surprise attack, led by the Islamist group Hayat Tahrir al-Sham, was the boldest rebel assault for years in the civil war that has been frozen.