More than 30 rebel factions have broken with the Western-backed Syrian opposition organisation and its military wing, according to a video statement posted on the Internet.
Though representing a small percentage of the rebel forces, the announcement by dozens of units from different areas across the country further undermines international efforts to build a pro-Western military force to replace President Bashar al-Assad.
The statement read online by rebel officer Ammar al-Wawi cited "the catastrophic failure" of the Syrian National Coalition (SNC) and its military wing, the Supreme Military Council (SMC).
It said the groups' withdrawal of support was precipitated by the foreign-based leadership's "marginalisation ... from the revolutionary force operating on the ground" and its "deviation from the path of the revolution."
Syria's opposition forces have been riven with factionalism since the 2-1/2-year revolt against Assad began. There have also been tensions between increasingly powerful Islamist groups and those that support a secular vision for a post-Assad Syria.
Earlier this week, some of the largest and most influential rebel factions, including the al Qaeda-linked Nusra Front, announced their rejection of the Western-backed opposition coalition and called for its reorganisation under an Islamic framework.
The groups which Wawi cited were considerably smaller and less influential than those units.
Friday's statement made no reference to Islamic law, but it went further than the earlier announcement by explicitly rejecting the military command of General Salim Idriss, who heads the SMC.
The statement also blamed the international community for failing to stop "crimes against humanity committed by the criminal Bashar along with terrorist gangs from Iran, (Iraqi Prime Minister Nuri) Maliki's militias and Hezbollah."
The sectarian dimension of the conflict has drawn in foreign fighters from neighbouring countries.
Thousands of Sunni militants have entered Syria to fight alongside the rebels, while Lebanese Shi'ite militant group Hezbollah and Shi'ite militias from Iraq have sent men to fight alongside Assad's forces.
Many Syrian opposition groups inside Syria, regardless of their ideological background, are skeptical and resentful of the Western and Gulf Arab-backed National Coalition, an umbrella organisation for opposition groups abroad.
Critics accuse it of not being transparent with funding and its political processes and of being out of touch with those living inside Syria, where more than 100,000 people have been killed and swathes of territory have been destroyed by combat and shelling.