Twenty prominent members of the Syrian National Council (SNC) have walked out over slow progress in bringing down the regime.
The SNC was hit after members walked away from the 270-strong body to create their own breakaway faction, the Syrian Patriotic Group (SPG).
The group, which contains secular and Islamist members, is headed by Haitham al-Maleh, a lawyer and former judge, who has fought the regime since 1970.
Other members include Kamal al-Labwani, an opposition leader who spent six years in jail; human rights lawyer Catherine al-Talli; Fawaz al-Tello, a member of the opposition with links to the Free Syrian Army; and Walid al-Bunni, who was formerly in charge of the SNC's foreign policy.
The group said: "Syria has experienced long and difficult months since the Syrian National Council was formed without it achieving satisfactory results or being able to activate its executive offices or adopt the demands of the rebels inside Syria.
"The previous mode of operation has been useless. We decided to form a patriotic action group to back the national effort to bring down the regime with all available resistance means including supporting the Free Syrian Army."
Tensions are set to rise between the SNC and the SPG, making the question of who will replace President Bashar al-Assad even more difficult.
The SNC was formed in Istanbul. It is headed by Burhan Ghalioun, a respected secular professor and prominent opposition figure.
Gahalioun has the support of the Muslim Brotherhood, Syria's largest opposition movement under both Assad and his late father, Hafez.