Veteran dissident George Sabra, a Christian former communist, was elected president of the Syrian National Council opposition bloc at a meeting in Doha on Friday, an AFP journalist said.
The SNC's 41-member general secretariat, itself newly elected, chose Sabra, who garnered 28 votes, as part of efforts to revamp the group working to oust President Bashar al-Assad.
Sabra, in his first statement as SNC chief, vowed to "work with other components of the Syrian opposition to accelerate the fall of the (president's) criminal regime."
Asked what he wanted from the international community, he said: "We have only one demand, and that is to stop the bloodbath and help the Syrian people chase out this bloody regime by providing us with weapons.
"We want arms," Sabra said three times.
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However, a major activist network quit the bloc on Friday amid divisions between the opposition, and other anti-Assad groups went ahead with a unity meeting in Doha even though the SNC had asked for a delay.
The SNC had sought to meet on Saturday after choosing a new chief, having already elected the secretariat, a third of them Islamists, and as it faced charges of not being representative enough.
"We requested a postponement of 24 hours -- we are in the electoral process," Ahmad Ramadan, a member of the new team, told AFP before Sabra was elected.
But the Local Coordination Committees, a major network of on-the-ground activists, said it had withdrawn from the SNC over its failure to adopt "serious and effective" reforms to make it more representative.
Other opposition groups, who were waiting at a hotel in the Qatari capital, decided to go ahead with their meeting brokered by Qatar and the Arab League on Friday evening, regardless of the SNC's demand for a delay.