By Mariam Karouny
BEIRUT (Reuters) - Islamist militants affiliated to al Qaeda seized the last remaining stronghold of Western-backed rebels in Syria's northwest province of Idlib on Saturday after days of fighting, rebels and a monitoring group said.
Backed by other hardline Islamist groups, the Nusra Front are waging a major military campaign against the Syria Revolutionaries' Front led by Jamal Maarouf, a key figure in the armed opposition to President Bashar al-Assad, after accusing him of being corrupt and working for the West against them.
The Nusra Front is al Qaeda's official affiliate in the Syrian civil war and was once one of the strongest insurgent groups fighting to topple Assad. But it has been overshadowed by the Islamic State, which has seized swathes of northern and eastern Syria and is now being targeted by U.S.-led air strikes
In the past few days, the Nusra Front captured several villages in the Jabal al-Zawiya region of Idlib province and on Saturday it entered the village of Deir Sonbol, the stronghold of the Revolutionaries' Front, forcing Maarouf to pull out.
"Dozens of his fighters defected and joined Nusra, that is why the group won," Rami Abdulrahman, head of the Syrian Observatory for Human Rights told Reuters.
A Nusra fighter confirmed the report, saying: "They left him because they knew he was wrong and delusional."
"He left his fighters in the battle and pulled out. Last night, we heard them on the radio shouting 'Abu Khaled (Maarouf) escaped, Abu Khaled escaped'," he added.
Maarouf's group is loosely defined as part of the "Free Syrian Army", a term used to refer to dozens of groups fighting to overthrow Assad. They have little or no central coordination and are often in competition with each other.
Hours after his withdrawal, a defiant Maarouf issued a video statement in which he vowed to continue the fight against Nusra and said his group would return to Jabal al-Zawiya.
"For a week now, Nusra Front has put the villages of Jabal al-Zawiya under siege (as if) they were the 'Noseiry' regime, " Maarouf said in the video, using a derogatory term for Assad's Alawite sect, which is an offshoot of Shi'ite Islam.
"I (want to) clarify why we pulled out of the villages of Jabal al-Zawiya. (It is) so that we preserve civilian blood because this group does not hesitate to kill civilians."
A source in a group affiliated to Maarouf denied that any fighters had defected to the Nusra Front.
The Syria Revolutionaries' Front is one of the biggest groups in the Western and Saudi-backed opposition to Assad.
The United States plans to expand military support to moderate opposition anti-Assad groups as part of its strategy to defeat the ultra-hardline Islamic State.
(Additional reporting Tom Perry; Editing by Gareth Jones)