Extremist group says Abu al-Hussein al-Husseini al-Qurashi was killed while fighting rival jihadists, names Abi Hafsan al-Hashimi al-Qurashi as new leader

Jamal Zeina split from group once known as Nusra Front earlier this year to set up a new hardline organization

Investigators for Human Rights Council attribute alleged rights abuses to Assad regime, Russian forces, al-Qaeda-linked fighters and Turkish-backed rebels

Fighting flares as Syrian regime and ally Russia bombard Idlib region, fueling humanitarian crisis and killing over 80

A handful of names stand out as possible successors to Islamic State chief, but experts say day-to-day operations won't be affected by leadership void

Withdrawal of jihadist group from Khan Sheikhoun in country's northwest marks significant loss, weakening opposition's grip on Idlib, its last major stronghold