(Reuters) - At least 45 civilians were killed and some 175 wounded when aircraft bombed a northern Syrian city controlled by Islamic State, as Bashar al-Assad's government stepped up air raids, residents and a monitoring group said on Friday.

Helicopters and war planes dropped barrel bombs -- steel drums full of shrapnel and explosives -- on residential and industrial areas in the city of al Bab and neighboring Qabaseen, northeast of Aleppo, on Thursday and overnight, locals said.

"People were going about scraping a living and there were no armed groups in the market, only poor people. Why is Assad killing us? May God bring vengeance on him," said Yousef al-Saadi, a resident of Qabaseen and a volunteer with the local civil defense group who was contacted on Skype.

Syrian state media did not report the strikes on al Bab, a city of around 100,000 people that has been a target of heavy government strikes since the start of U.S.-led military campaign against Islamic State, an Islamist militant group, in Syria in late September.