By Halit Suleyman

ALEPPO, Syria 

At least 15 civilians were killed Friday evening in barrel-bomb attacks carried out by regime helicopters in opposition-held parts of Syria’s city of Aleppo.

A civil defense official in Aleppo, Ibrahim Abu Leith, told Anadolu Agency that regime helicopters had bombed the opposition-held residential neighborhoods of Katirci and Tarik el-Bab.

Dozens of civilians were also injured in the attacks, he said.

In recent days, regime helicopters -- along with Russian and Syrian warplanes -- have struck a number of marketplaces, hospitals and civil-defense centers in opposition-held parts of the war-battered city.

Russian jets have also struck the strategic Castillo Road, which represents the opposition’s only means out of Aleppo, along with the Anadan, Hreytan and Kafr Hamrah areas.

Syria has been locked in a vicious civil war since early 2011, when the Bashar al-Assad regime cracked down on pro-democracy protests -- which erupted as part of the "Arab Spring" uprisings -- with unexpected ferocity.

Since then, more than a quarter of a million people have been killed and more than 10 million displaced across the war-battered country, according to the UN.

The Syrian Center for Policy Research, however, put the death toll from the six-year conflict at more than 470,000 people.

* Anadolu Agency correspondent Can Erozden contributed to this report from Ankara