Nearly 50 fighters have been killed in three days of clashes between jihadists and mainstream rebels in Aleppo, the Syrian Observatory for Human Rights said on Saturday. It said the fighting erupted on Thursday between militants of the Al-Qaeda-linked Islamic State of Iraq and the Levant (ISIL) and a battalion linked to the Arab- and Western-backed Free Syrian Army (FSA), both of which are fighting to topple President Bashar al-Assad.