Top Syrian rebel leader Zahran Allouch was killed in an airstrike in the suburbs of the Syrian capital on Friday. The Jaish al-Islam group has been fighting to overthrow President Bashar al-Assad’s government. Peace talks were to be held between the Syrian government and opposition representatives in Geneva next month, Associated Press reported, and Allouch’s death will be a blow to insurgents. The Syrian Observatory for Human Rights said an airstrike hit a meeting near Otaya, a suburb in Damascus, killing several people including Allouch. Reuters reported that it was a Russian airstrike that killed the rebel leader, whose group had been backed by Saudi and Turkish investors. The rebel group has appointed Essam al-Buwaydhani, a field commander known as Abu Hammam, as their new leader.

Russian airstrikes in Syria started in September, for the main purpose of defeating Islamic State militants. While Russia supports Assad, and reports have said that many rebels fighting Assad’s regime have also been killed in these strikes. Reuters reported that Russian planes fired at least 10 missiles at the site in Damascus where Allouch was killed.

Experts say Allouch’s death may help Assad gain better control of the area. Jaish al-Islam has been running the Eastern Ghouta area since 2013. Reuters said that Allouch was ideologically different from Islamic State and the al-Qaeda, and believed in a more moderate form of Islam. He fought against many militant Islamists and drove them out of his territory and has also been responsible for locking up dozens of jihadists.