Syrian rebels launched a dawn assault on Saturday on a strategic airbase in the north of the country, trying to disrupt strikes by warplanes and helicopters which pound rebel-held towns and give the regime of Syrian President Bashar Assad a major edge in the civil war.

The assault, reported by activists, comes a day before the start of a key international conference in Qatar at which the United States and its allies aim to reorganise the opposition's political leadership and unite their ranks.

The leadership-in-exile has been widely seen as ineffective and out of touch with rebel fighters on the ground.

Rebel forces attacked the Taftanaz airbase early on Saturday morning in fighting with government forces that continued into the afternoon, the anti-regime activist Syrian Observatory for Human Rights said.

Joining Syrian rebels in the attack were fighters from Jabhat al-Nusra, an al-Qaida-inspired Islamic militant group made up of foreign jihadis, according to the Observatory.

Al-Nusra fighters, who are considered among the most experienced and disciplined among the opposition forces, have led attacks on other airbases in the north in past months.

The Taftanaz base mainly houses military helicopters, near the main highway between the capital Damascus and the northern city of Aleppo, where rebels and the military have been battling for control for months.

Online activist videos claimed to show the battle, with rebels firing rockets and mortars, and smoke rising over buildings and an airstrip area.

An activist speaking in the video identifies it as an attack by rebels and Jabhat al-Nusra on the base.

The videos appeared genuine and are consistent with other Associated Press reporting in the area.

The capturing of the base - and holding on to it - would be a major achievement for the rebels, who often complain they are outgunned by government forces.

Air strikes have been one of the most effective and feared weapons of the regime in the civil war.

Activists say more than 36,000 people have been killed during Syria's 19-month-old conflict, which began in March last year as a largely peaceful uprising, but has transformed into a brutal civil war.