BEIRUT — Syrian rebels launched a dawn assault Saturday on a strategic airbase in the north of the country, trying to disrupt strikes by warplanes and helicopters that pound rebel-held towns and give the regime of President Bashar al-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 reorganize 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.

Rebels forces attacked the Taftanaz airbase early 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 said the show the battle showed rebels firing rockets and smoking rising over buildings and a airstrip. An activist speaking in the video identifies it as an attack by rebels and Jabhat al-Nusra on the base.

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

Airstrikes have been one of the most effective and feared weapons of the regime in the civil war. Rebels managed to seize control of a pocket of territory around Aleppo, but government warplanes and helicopters continue to blast rebel-held towns from the air. In the fierce fighting over Aleppo itself, warplanes almost daily swoop in to strafe or bomb rebel-held neighborhoods.

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.

Several attempts for a truce in the fighting have failed, including the U.N.-supported four-day ceasefire that was meant to coincide with a major Muslim holiday last week, leaving the international community at a loss for ways to end the war.

Secretary of State Hillary Clinton on Wednesday called for a major leadership overhaul and suggested Washington would handpick more representative leaders, including those fighting the regime. The opposition conference the Qatari capital, Doha, starts on Sunday.