BEIRUT, Feb 6 (Reuters) - Rebels announced a new military campaign in the northern Syrian province of Aleppo on Thursday, a few days after government forces stepped up air attacks in a bid to recapture territory and drive residents out of opposition-held areas.
The largest Syrian rebel coalition, known as the Islamic Front, joined forces with the Nusra Front, al Qaeda's franchise in Syria, to launch an assault dubbed "The promise of truth approaches", a reference to a Koranic verse about Judgment Day.
President Bashar al-Assad's forces recently mounted a series of attacks on Aleppo city, once Syria's business hub, using barrel bombs - oil drums or cylinders packed with explosives and metal fragments.
They are a particularly indiscriminate weapon activists say is being used to push out civilians as the army tries to seize the initiative on the long-stalemated Aleppo battlefront.
"All military forces in their bases should head to the front lines, otherwise they will be questioned and held accountable," a joint rebel statement said.
It warned residents near checkpoints and bases held by Syrian government forces to leave in the next 24 hours, saying the areas would be the insurgents' main targets.
Forces loyal to Assad have been making small gains on rebel-held parts of Syria's second city, advances which many opposition sources blame on weeks of rebel infighting that has killed over 2,300 combatants.
The Islamic Front and some of its secular rebel allies are trying to oust an al Qaeda splinter group, the Islamic State of Iraq and the Levant, with whom they have ideological and territorial disputes.
Syria's nearly three-year conflict began as popular protests against four decades of Assad family rule but changed into armed insurgency under a security force crackdown.
Now the major Arab state is in a full-scale civil war that has killed more than 130,000 people and forced over 6 million - more than a quarter of the population - to flee their homes.
Since government forces unleashed the barrel-bombing campaign on rebel-held Aleppo last week, residents have been leaving in droves to seek refuge in government-held parts of the divided city.
Others have fled to Turkey, where many have been held up at the border crossing as camps near Aleppo faced overcrowding. (Reporting by Erika Solomon; Editing by Mark Heinrich)