Syria's Muslim Brotherhood may be President Bashar al-Assad's best-organised political adversaries, but they are also loathed by some dissidents who accuse them of trying to dominate the opposition, backed by funds from Qatar.
The accusations date back to the start of uprising against Assad, but came to a head on March 19 after the election of rebel prime minister Ghassan Hitto, with some activists saying his selection was "pushed" by the Brotherhood.
In late March, some 70 dissidents sent a letter to the Arab League criticising "the dictatorial control exercised by one of (the opposition's)... currents over its decisions and actions, and the flagrant hegemony of diverse Arab and regional players."
Immediately after Hitto was elected in a meeting of the key National Coalition grouping in Istanbul, a dozen prominent opponents froze their membership in the organisation.
Among them was Kamal al-Labwani, an influential liberal and one of the Brotherhood's most outspoken critics.
"The Brotherhood leads all the decision-making in the Coalition. They control the committees linked to arming (the rebels) and humanitarian assistance," Labwani told AFP.
"They appear to be just a few in the Coalition, but they buy the other members out thanks to the money they receive from Doha and Ankara. They are trading in influence," he said.
London-based Ali al-Bayanouni, the Brotherhood's deputy political chief, rejected the accusations.
"Our role in the Coalition has been greatly exaggerated, and we are not financed by any state," he told AFP, saying the group's funding comes from "members and supporters, from Syria and elsewhere".
"We represent just 10 percent of the Coalition. How can they say we control everything?"
Critics of the Brotherhood fear the group may harvest the fruits of the anti-regime revolt, as they have in Egypt.
"In all the Arab Spring countries, the revolution was stolen by the same people: the Muslim Brotherhood. We are dying on the frontlines, while they take the influential positions," a rebel fighter in the coastal province of Latakia told AFP.
Founded in Egypt in 1928, the Brotherhood seeks to spark an Islamic renaissance and challenge the Western political model.
The movement emerged in Syria in the 1930s, later spearheading a revolt against Assad's father and predecessor, Hafez al-Assad, who brutally crushed the uprising in the city of Hama in 1982. Between 10,000 and 40,000 people were killed, according to rights groups.
The group is outlawed in Syria, with members subject to execution.
"They believe that they are the natural leaders of Syria, they believe that... their time has finally come and that they represent the nation better than anybody else," said Joshua Landis, a Syria expert at the University of Oklahoma.
"That self-assurance is resented of course by all the other groups... The Brotherhood are the presumed winners, and that is why they are targeted."
Analysts and dissidents admit that the Brotherhood are Syria's best organised opposition group. They have a hierarchy, offices, a website and even a newspaper.
"Qatar and Turkey support them because they are the only institutional party that has any chance of organising Syria" should Assad fall, Landis told AFP.
"They are well-organised politically, militarily and financially. That's why they are taking over," said a rebel fighter in the northern city of Aleppo.
Damascus accuses the Brotherhood of acting as instruments of Qatar and Turkey, where their chief, Mohammad Riyad al-Shaqfa, is based.
And though the group pays lip service to a civil state based on human rights, among anti-regime activists "there is a deep suspicion that they are using democracy to come to power, and then once they come to power, they will use the laws in order to suppress their critics as we see today in Egypt," Landis added.
The West may also prefer to work with the Brotherhood, which is more moderate than jihadists loyal to groups such as the Al-Nusra Front, opponents say.
And the Brotherhood is confident they have real support on the ground too.
"When there are democratic elections in Syria, we shall see who wins the majority," Bayanouni said.