Progressive Socialist Party leader Walid Jumblatt Monday criticized last week's killing of a powerful Syrian rebel commander in a government airstrike outside Damascus. Jumblatt, who backs rebels fighting to unseat President Bashar Assad, said the killing of Jaish al-Islam chief Zahran Alloush also killed efforts to negotiate an end to the Syrian crisis. "He (Alloush) fought the Assad regime with all means possible, even with reprehensible ways. This is because the regime used all destruction and methods of torture available against Syrian civilians," Jumblatt wrote on Twitter. "The assassination of Zahran Alloush... is the assassination of the... political solution for the so-called transition". Jumblatt's Druze rival, Tawhid Party Chief Wiam Wahhab, responded to the comments by accusing Zahran of criminality. "Commander of the Army of Islam Zahran Aloush is a big criminal, you must be crying over the hundreds of students who were killed in Damascus schools and universities (by Alloush's forces)," Wahhab said. The Army of Islam was one of the most influential armed groups invited to broad-based opposition talks in Riyadh earlier this month. The group fought ISIS, but is accused of sectarian killings. Alloush had called for the extermination of Shiites from Damascus. He was killed in an airstrike Friday claimed by the Syrian government, although rebels accuse Russia of being behind the strike.