Rebels in Syria say they have launched a major offensive to capture a key airbase in the north of the country, BBC News reported.

Video posted on the internet showed fighters attacking the Taftanaz base in an attempt to control a strategic zone between Syria's two biggest cities, Aleppo and Damascus.

The attack comes a day before a crucial opposition meeting in Doha, Qatar.

It also follows the apparent murder of a number of Syrian troops by rebels, which drew international condemnation.

The attack on Taftanaz took place as dawn broke, with five different units of rebel fighters opening fire with multiple rocket launchers, mortars and other weaponry, according to the video.

Rebel forces are reported to have taken control of the main roads in much of the area south-west of Aleppo.

The video said the rebel groups involved included several brigades of the Free Syrian Army, but also the radical Islamist al-Nusra Front.