But after dozens of countries recognized the new group as the successor to Assad’s regime, it, too, has failed to win influence. It missed its own deadline last week to name an interim prime minister, and U.S. engagement with the organization, which reached its height prior to the U.S. presidential election in November, dropped off after the group’s leader, Sheik Mouaz Khatib, criticized the U.S. designation of the Nusra Front as an international terrorist group that is indistinguishable from al Qaida in Iraq.

Syrian activists say that the U.S. plan to diminish the role of Islamist groups in the anti-Assad fighting instead has resulted in the Islamists gaining more power.

“The Islamist battalions are the only battalions that work on the ground,” said Omar Shakir, an anti-government activist from Homs, the country’s third largest city.

He said U.S. efforts to support the military council in Homs dried up after commanders there refused to cut links to Islamist groups, as the United States demanded.

“The Islamist battalions have their own sources for money and weapons, they are really fighting well against the regime,” Shakir said. “So after the U.S. cut the support, the military council became powerless and most fighters are joining Islamist battalions.”

Those battalions, which include Nusra and another Islamist brigade, Ahrar al Sham, have been at the forefront of the fighting across Syria. More moderate Islamist groups, such as the Farouq Brigades and Liwa Tawhid, both of which are believed to be allied with the Syrian Muslim Brotherhood, also operate across the country.

Nusra is believed to have as many as 5,000 men under arms, and Sham is thought possibly to be larger, making the Islamist-led groups the largest fighting organizations of the multi-faceted Syrian opposition.

The United Nations has said that more than 60,000 people have died in violence since the anti-Assad uprising began in March 2011.