Al-Nusra Front fighter in Syria
Al-Nusra Front fighter in SyriaReuters

Islamist rebels captured four crew members of a regime helicopter which crashed in the Idlib province of northwest Syria on Sunday, while a fifth serviceman was killed, a monitor said, reported AFP.

"A regime helicopter was forced to land in the region of Jabal al-Zawiya in the northwest, which is a bastion of (Al-Qaeda's Syrian affiliate) Al-Nusra Front," Rami Abdel Rahman, head of the Syrian Observatory for Human Rights, told the news agency.

"Four of the crew were captured and a fifth man was killed by armed men in a neighboring village," he added.

Abdel Rahman said the Al-Nusra Front held two of the servicemen, including the helicopter's pilot.

Official Al-Nusra Front accounts on Twitter published photos and videos with the caption "Helicopter pilot in the hands of jihadists," according to AFP.

The images depict the bandaged pilot sitting in front of Al-Nusra Front's official flag.

"To the Muslim children, to their mothers, who died two days ago because of their chlorine attack," a bearded fighter says in the video, pointing to the pilot.

On March 17, a family of six died in Idlib province after a regime gas attack on the village of Sarmin. Opposition forces accused the regime of using chlorine, a toxic agent that can be considered a chemical weapon.

Two other servicemen from the helicopter crash were captured by another Islamist group, and at least one more crew member was believed to be on the run, Abdel Rahman told AFP.

Regime helicopters are often used to drop crudely constructed barrel bombs on rebel-held areas.

Pictures provided by the Observatory showed groups of men gathering around a damaged helicopter lying on its side on a rocky hilltop.

Syrian state television confirmed a military helicopter had crashed in Idlib, saying it was due to a technical failure and that search efforts were underway to locate the crew.

Al-Nusra Front has been an official branch of Al-Qaeda since April 2013, and dominates a swathe of northwest Syria despite months of international airstrikes.

As well as fighting President Bashar Al-Assad's regime, the group has clashed with Western-backed rebels and its jihadist rival the Islamic State (ISIS) group. Last November, Al-Nusra and ISIS agreed to work together.

Al-Nusra Front recently reaffirmed its allegiance to Al-Qaeda and denied any plan to break away and become a more internationally acceptable rebel force, amid speculations on Internet social networks of a split between the jihadist allies.