DAMASCUS: Syrian rebels said on Saturday that they had launched a major assault against a northern airbase used to deploy regime air power, on the eve of a crucial meeting to decide the future of the opposition.

The attack on the Taftanaz base, from where helicopter gunships raid opposition positions and rebel-held areas, comes after regime forces this week launched an unprecedented wave of air strikes in a bid to reverse rebel gains.

A video posted on the Internet said eight battalions were taking part in the attack, including the radical Islamist Al-Nusra Front, and showed a missile launcher mounted on the back of a pick-up truck firing on regime positions.

The Syrian Revolution General Commission (SRGC), a network of activists on the ground, said an operation had begun “to liberate the Taftanaz airbase”.

The Syrian Observatory for Human Rights (SOHR), a Britain-based watchdog, said “heavy fighting” had broken out near the base, in Idlib province where rebels have made significant gains this week.

The rebels seized an air defence position at Duwila in Idlib earlier on Saturday, killing an army officer and wounded eight rebel fighters in the ensuing fighting, the Observatory said.

The rebels fled under attack from the air after seizing arms and ammunition from the post.

The rebels made other gains near Damascus by seizing a police station, a municipal building and a hospital in the town of Douma, northeast of the capital, after fighting that killed 21 soldiers, the Observatory said.

The fresh clashes came as Syria's political opposition prepared for key talks starting Sunday in Qatar, where the United States (US) is expected to push for a new umbrella organisation to unite the country's fractured regime opponents.

Reports have emerged that Washington will press for an overhaul of the opposition and its main representative body, the Syrian National Council (SNC), with long-time dissident Riad Seif touted as the potential head of a new government-in-exile dubbed the Syrian National Initiative.

The SNC lashed out at US interference on Friday, accusing Washington of undermining the country's revolt and “sowing the seeds of division” by seeking the overhaul.

Washington denied it was trying to interfere, insisting it was simply seeking to ensure that more voices were heard.

The rebels consolidated their hold on the area Friday by forcing regime troops out of their last position, taking control of a key crossroads where the roads to commercial hub Aleppo from Damascus and from the Mediterranean coast meet.

Nationwide, 181 people were killed in violence on Friday, according to the Observatory, which relies on a network of activists and medics in civilian and military hospitals for its figures.

It says more than 36,000 people have been killed since the uprising against President Bashar al-Assad's rule broke out in March 2011 as a protest movement inspired by the Arab Spring before escalating into an armed rebellion.