BEIRUT (Reuters) - Syrian rebel rocket fire on government-controlled areas of Aleppo killed 50 people over the weekend, a monitoring group said on Monday, the eve of an election in which rebels have warned they will step up attacks on state targets.

The Syrian Observatory for Human Rights said the death toll from the attacks by the Islamist rebels included nine children.

Another 13 people were killed overnight when President Bashar al-Assad's forces dropped four barrel bombs - crude explosives which cause widespread damage - from helicopters into rebel-held districts of the city, the UK-based Observatory said.

Fighting in Aleppo, which was Syria's commercial hub before the three-year conflict erupted, has escalated in recent weeks after Assad's forces consolidated their control in central Syria and the last rebels retreated from the center of the city of Homs.

(Reporting by Dominic Evans; Editing by Hugh Lawson)