Al-Qaeda-linked group al-Nusra Front is consolidating its power in territory across Syria as Western air strikes focus on rival jihadist group Islamic State (Isis), experts have said.

The group now controls territory stretching from the Golan Heights on the Syrian/Israeli border, through central Syria to the country's border with Turkey in the north.

With attention focused on IS, which has waged a high-profile online propaganda campaign, al-Nusra has in recent weeks pushed back moderate Western-backed rebel groups in Syria's Idlib province.

"The Nusra Front will most likely outlast Isis in Syria, and will represent a severe and existential threat to the aspirations of the Syrian people in terms of a pluralistic, democratic society," Fawaz A Gerges, director of the Middle East Center at the London School of Economics, told AP.

A Syria-based western diplomat told the agency that al-Nusra stepped up its campaign against moderate rebel groups after the US-led coalition began targeting IS positions, as well as those of the allegedly al-Nusra affiliated Khorasan group, in September.

Earlier this month, the group pushed Western-backed rebels from an airbase west of Aleppo.

The Hazm movement, a rebel group that had allegedly received arms and training from the US, disbanded this year after a series of punishing defeats suffered at the hands of al-Nusra in the vicinity of Aleppo.

Some of the group's fighters have reportedly joined Islamist groups.

Al-Nusra claimed that it seized US weapons when it overran Hazm's centre of operations.

Recently, Qatar reportedly offered to provide al-Nusra with arms and funding if it severed ties with al-Qaeda, and turned its guns against former allies IS.