Illustrating their plight, FSA commanders say that entire units have gone over to al-Nusra while others have lost a quarter or more of their strength to them recently.

“Fighters feel proud to join al-Nusra because that means power and influence,” said Abu Ahmed, a former teacher from Deir Hafer who now commands an FSA brigade in the countryside near Aleppo. “Al-Nusra fighters rarely withdraw for shortage of ammunition or fighters and they leave their target only after liberating it,” he added. “They compete to carry out martyrdom [suicide] operations.”

Abu Ahmed and others say the FSA has lost fighters to al-Nusra in Aleppo, Hama, Idlib and Deir al-Zor and the Damascus region. Ala’a al-Basha, commander of the Sayyida Aisha brigade, warned the FSA chief of staff, General Salim Idriss, about the issue last month. Basha said 3,000 FSA men have joined al-Nusra in the last few months, mainly because of a lack of weapons and ammunition. FSA fighters in the Banias area were threatening to leave because they did not have the firepower to stop the massacre in Bayda, he said.