International outrage over those killings, which the Syrian government said were carried out by rebels, has injected new urgency into diplomatic efforts to settle the Syria conflict at the Security Council. There, diplomats were negotiating privately on Friday over a new resolution to force the antagonists to honor a cease-fire and peace plan engineered by Mr. Annan, the special envoy from the United Nations and the Arab League. A vote on that resolution is likely next Wednesday.

The diplomacy seemed a world away, and possibly too late, when viewed through the prism of the anti-Assad fighters, who have driven much of the Syrian military forces from certain rural zones in the northern mountains, carving out small but mostly stable areas now under their de facto control, though these areas still face shelling and attack from the air by Mr. Assad’s military.

As they have realized tactical success, the anti-Assad fighting groups, once underground, now face a problem common to armed uprisings.

At least 80 different fighting groups operate in Idlib alone, the fighters said, most of which began as small personal networks or groups of army defectors, and have since grown.

The groups sometimes share names and often operate in the same areas. And as they have added members and sought more weapons and external support, some of them have found themselves competing for resources and frustrated with Syrians who claim leadership positions in the opposition and do not fight, but disburse funds that many fighting groups say they do not receive.

Mr. Afara, for example, said money funneled through the Muslim Brotherhood was not shared with fighting groups seen as secular, which angered fighters who had turned back the Assad military at great cost, and now are told they do not match a foreign donor’s ideal.

“We tell them, ‘We are not brothers?’ ” said Mr. Afara, who leads a unit in a larger group called the Idlib Martyrs’ Brigade. “How? We are Muslims, and we want a full popular revolution, with Muslims and Christians and Druze.”