The main opposition Syrian National Council, under pressure to unite and bring in all parties, has elected a new leadership with Islamists heavily represented, SNC officials said on Thursday.

They said a president of the opposition coalition would be chosen on Friday, after the 40-member general secretariat was elected overnight at a meeting in the Qatari capital.

The secretariat is tasked with electing 11 members to appoint a successor to outgoing president Abdel Basset Sayda.

The process has been delayed until Friday to allow four members representing women and minorities to be added to the secretariat ahead of the vote, the officials said.

Sayda remains a secretariat member but other prominent figures such as his predecessor Burhan Ghalioun, George Sabra and Riad Seif do not figure in the new list, effectively ruling them out as SNC president.

Some 400 SNC members voted from 29 lists of groups opposed to Syrian President Bashar al-Assad ranging from liberals to the Muslim Brotherhood, as well as ethnic minorities and tribes.

Islamists, including at least five Muslim Brotherhood members, account for around a third of the new secretariat, with the Kurdish and Assyrian minorities also represented but no women.

"Under our statutes, we can add four members. So we will designate two women and two members representing the religious minorities," Ahmad Ramadan, a member of the new team, said.

SNC officials said a Christian and an Alawite, a member of the Shiite sect to which Assad belongs in Sunni-majority Syria, could thus be added to the team.

Arab League chief Nabil al-Arabi, who has urged the opposition to close ranks, is due to take part in broader meeting on Thursday called by his organisation and hosts Qatar of a wide range of Syrian 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 on Wednesday before travelling to Doha.

But the SNC said the "only body that can form a transitional government is a general national congress bringing together all political opposition forces, in which the SNC would hold the biggest share."

The SNC statement appeared to challenge an initiative proposed by prominent dissident Seif to unify the opposition which is expected to top the agenda of Thursday's broader meeting.

The SNC also called for "holding the national congress in Syria on liberated territory when that is possible," and insisted that "a transitional government would not be announced before firm guarantees of international recognition."

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 opposition to reshape into a widely representative government-in-exile.

But the SNC -- which was set up six months after the uprising against the Assad regime erupted in March last year -- has accused Washington of undermining the revolt and "sowing the seeds of division."

Sayda has insisted that the group must remain the "cornerstone" of any revamped Syrian opposition force.