The rebels are led by the Hayat Tahrir al-Sham group, or HTS, which has its origins in al-Qaida and is considered a terrorist organization by the United States and the United Nations. Al-Golani, has sought to recast the group as a moderate and tolerant force. “Golani has made history and sparked hope among millions of Syrians,” said Dareen Khalifa, a senior adviser with the International Crisis Group. “But he and the rebels now face a formidable challenge ahead.” The U.N.’s special envoy for Syria, Geir Pedersen, called Saturday for urgent talks in Geneva to ensure an “orderly political transition.” The Gulf nation of Qatar, a key regional mediator, hosted an emergency meeting of foreign ministers and top officials from eight countries with interests in Syria late Saturday. They included Iran, Saudi Arabia, Russia and Turkey. Majed al-Ansari, Qatar’s Foreign Ministry spokesman, said they agreed on the need “to engage all parties on the ground,” including the HTS, and that the main concern is “stability and safe transition.”