The death of Syrian rebel leader Zahran Alloush is being seen a major blow to a tenuous peace process, with the opposition's interim leader warning that other rebel commanders and political opponents could also be targeted for assassinations.
Alloush, the leader of the Jaysh al-Islam group, was killed on Friday in an air strike claimed by Syrian government forces.
"They killed a man who was going to play a crucial role in Syria," Ahmad Tumah, the designated opposition prime minister, told Al Jazeera on Saturday.
"The death of Zahran could lead to more targeted killings of prominent opposition commanders and politicians."
Tumah accused the government of President Bashar al-Assad of deflecting attention from "the fight for political right and against tyranny" to a fight against the Islamic State of Iraq and the Levant (ISIL), which he said is the main concern of the international community.
Tumah also said that while he still intends to attend the peace talks in Geneva, Switzerland, in January, Assad should not have any role in the future of Syria.
In a separate statement, the National Coalition for Syrian Revolutionary and Opposition Forces, an umbrella organisation headed by Tumah, condemned Zahran's killing, describing it as "a clear victory for terrorism and ISIL".
"It weakens the free army factions that confronted terrorism and undermined its foundations," the statement said.
"The attack is also an attempt to abort the UN efforts of a political settlement."
Jaysh al-Islam is said to have named Abu Hammam Bouwaidani as the successor of Alloush.