Syria's main umbrella opposition group, under US pressure to broaden its representation and urged by the Arab League to present a united front, began voting in a new leadership in Doha on Wednesday.
Some 400 members of the Syrian National Council were to choose from 29 lists of opposition groups ranging from liberals to the Muslim Brotherhood, as well as ethnic minorities and tribes.
As voting for a new 40-member general secretariat got under way in the Qatari capital, Arab League chief Nabil al-Arabi urged the opposition to unify ranks against what he said was President Bashar al-Assad's crumbling regime.
"It is important to unify the opposition's visions, especially because everyone knows that the regime in Syria will not remain for long and one day there will be a new situation in Syria," Arabi told reporters in Cairo.
Arabi is due to take part in broader meeting on Thursday called by the Arab League and Qatar, also in Doha, of a wide range of Syrian opposition groups.
Preparations must start for a transitional government to be ready when "there are changes on the ground," in Syria, the Arab League chief said in Cairo before heading out to Doha.
The new SNC secretariat general, once elected, is expected in turn choose a politburo and a president to replace the group's chief Abdel Basset Sayda, who assumed the post in June.
The SNC, which has been meeting in Doha since Sunday, has already agreed to include 13 new groups in its structure as it bids to become more inclusive.
But US State Department spokeswoman Victoria Nuland on Monday appeared to play down the move, saying restructuring required more than numbers.
"We've said from the beginning... that we expect that the SNC itself will be part of the opposition structure that emerges from the Doha process... but that other groups in addition to the SNC will also be represented."
US Secretary of State Hillary Clinton last week called the SNC unrepresentative of opposition forces on the ground and said it "can no longer be viewed as the visible leader of the opposition."
Washington wants the Syrian opposition to reshape into a widely representative government-in-exile, and appears to be in favour of an initiative tabled by prominent dissident Riad Seif.
The SNC - which was set up six months after the uprising against the Assad regime erupted in March last year - has however accused Washington of undermining the revolt and "sowing the seeds of division."
Seif's initiative to unite all Syrian groups opposed to Assad is expected to top the agenda of Thursday's broader meeting.
But the proposal has encountered reservations from some SNC members.
SNC chairman Sayda has insisted that the group must remain the "cornerstone" of any revamped Syrian opposition force.
And his predecessor Burhan Ghalioun voiced concern that Thursday's meeting was seeking to abolish the council.
"The council rejects taking part in a framework that aims to kill it off," Ghalioun told AFP.