ALEPPO - Several thousand Syrian rebels on Thursday launched what they said would be a decisive battle for control of the strategic northern city of Aleppo.“Tonight, Aleppo will be ours or we will be defeated,” Abu Furat, a rebel commander, told AFP.His announcement came after more than 300 people were killed nationwide on Wednesday in what the Syrian Observatory for Human Rights said was the bloodiest day of the 18-month conflict so far.An AFP correspondent saw dozens of rebels grouping in Aleppo’s northern Izaa quarter and firing mortars.The city has seen fierce fighting since July, when rebels launched an offensive to capture the commercial capital. After some early successes, the rebel campaign slowed because of a shortage of ammunition.At least seven civilians were killed on Thursday in the northern metropolis as troops pummelled districts across the southwest and the east, the Britain-based Observatory said.The violence came after a car bomb exploded at an army checkpoint overnight in the northwest province of Idlib, about 25 kilometres (15 miles) south of Aleppo on the highway to Damascus.Rebels then attacked the checkpoint and fierce clashes raged, the watchdog said.In what appeared to be the same attack, a military source said clashes erupted overnight at a checkpoint in the same area after a minibus exploded.“When we saw the bus with just one driver and no one else in it, we thought it was suspicious and told him to stop. He didn’t and when we shot the driver the bus veered off the road and exploded,” the source told AFP.A large rebel force then attacked the checkpoint, according to the source, who said the fighting lasted until 7:30 am (04H30 GMT) when the rebels withdrew.The Observatory also reported that unidentified attackers blew up an oil pipeline in the northeast province of Hasaka, Syria’s main oil-producing region.In Idlib province, five civilians, including four children, died in army bombardment of Khan Sheikhun, according to the Observatory.Activist footage posted on YouTube showed pandemonium in the town, as men formed lines in a race to move chunks of rubble and the crowd began shouting as a small limp girl was lifted up and handed to a grey-haired man.The authenticity of the video could not be verified independently.At least 59 people - 38 civilians, 16 soldiers and five rebels - were killed nationwide on Thursday, the watchdog said.More than 30,000 people have been killed in Syria since the beginning of the revolt, said the Observatory, which gathers its information from a network of activists, doctors, lawyers and other sources on the ground.