Syria National Council to decide on unity leadership
The Syrian National Council is facing a key decision on whether to join other groups in a more unified opposition.
The proposed Syrian National Initiative aims to merge the disparate military and political groups to form a credible alternative to the Assad government.
Western and Gulf states have been pushing for such a body, which would act as a conduit for humanitarian - and possibly military - aid.
Meanwhile, the UN said 11,000 Syrians have fled in the past 24 hours.
UN officials meeting in Geneva said the increased rate of refugees reflected the deteriorating situation in Syria.
Among those fleeing, 9,000 went to Turkey, bringing the total number of Syrians there to 120,000.
Turkish news agency Anatolia said dozens of defecting Syrian army officers, including two generals and 11 colonels, had arrived in Turkey on Friday.
Aid officials at the Geneva meeting warned that 2.5 million Syrians now need humanitarian aid.
The Damascus government has strictly limited the presence of foreign aid agencies.
Activists estimate that more than 35,000 people have been killed since the uprising against President Bashar al-Assad began in March last year.
The opposition meeting, in the Qatari capital Doha, is taking place under the auspices of the Arab League, with Western powers from the international Friends of Syria group also attending.
So far Syrian National Council, itself an umbrella group, has been the most prominent opposition in the uprising, but has failed to produce a united front.
It has also been criticised for the fact its members are largely based outside Syria.
The US has said it wants to set up a broader opposition group in which the SNC's influence is diluted.
The Syrian National Initiative, proposed by prominent dissident Riad Seif, would replace the council, bringing together Syria's exiled and internal opposition and channelling foreign aid.
But the BBC's Jim Muir, in Doha, says the SNC is wary of signing up as a minority element in a new leadership without guarantees that the new body will be given enough support needed to defeat the regime.
The SNC, which has been holding its own talks in Doha, will elect a new executive and president on Friday, before deciding whether to back the initiative.
If it does not, says our correspondent, it risks being heavily blamed for pursuing its own interests above those of the people.
Such a move would open a stark rift in the opposition, he adds, especially between "insiders" who are strongly represented in the new leadership plan, and those who have been in exile for years.
Mr Seif said opposition leaders had made progress on the first day of talks, and that some SNC members had indicated their acceptance of a plan to set up a new leadership group composed of 60 members.
Veteran opposition figure Haytham al-Maleh told AFP news agency: "We hope we can reach an agreement [on Friday] after the Syrian National Council has succeeded in selecting a new leadership."
Burhan Ghalioun, ex-leader of the SNC outside Syria, said the atmosphere was "positive" and that failure was "forbidden".
The meeting on aid access in Geneva comes after the head of the International Committee of the Red Cross (ICRC) said the organisation could not cope with Syria's growing needs.
There are currently "a lot of blank spots", and an unknown number of people were not getting access to the aid they needed, said Peter Maurer.
The ICRC has not been able to get to certain parts of the country, he added, giving as an example the city of Aleppo, which has been badly hit by violence in recent months.