Syrians inspect the site where a barrel bomb dropped by an air force helicopter exploded in Saraqeb in northwestern Syria on July 20, 2013.

While the use of chemical weapons in Syria made the world sit up and take notice, conventional weapons continue to wreak havoc on the country's civilian population.

A crude but effective weapon has seen a resurgence in the conflict in recent days — the barrel bomb. The imprecise, incendiary weapons — oil barrels or cylinders filled with petrol, nails and TNT — are rolled out of low-flying helicopters.

The regime bombarded Aleppo, Syria's largest city, for four straight days this week, according to rebels. Its use of barrel bombs in the aerial assault claimed massive casualties, with nearly 200 people reported killed.

In one instance, a witness said a barrel bomb was dropped near a food distribution line, killing about 30 people, including a one-year-old child.

"A helicopter came, and suddenly out of nowhere a barrel hit this area," the witness told NBC.

"About 30 people died, including women and children who were waiting their turn so they can get the bread."

The bombing campaign in Aleppo is believed to be a show of might by Syrian President Bashar al-Assad ahead of peace talks, to be held in Switzerland in January.

It's not the first time that the use of barrel bombs has been documented in Syria. In August 2012, Syrian conflict blogger Eliot Higgins published images of what appeared to be an oil barrel that rolled from a helicopter and exploded in Aleppo.

Reports have trickled in over the last 18 months of barrel bombs being used elsewhere, including in Qusayr in late August 2012, and again in Aleppo last year.

Conflict reporter C.J. Chivers also documented the puzzling use of homemade bombs by the Syrian army for The New York Times' At War blog last October. 

US State Department spokeswoman Victoria Nuland acknowledged the use of barrel bombs in December 2012, calling them "an incendiary bomb that contains flammable materials."

Protocol III of the 1980 Convention on Conventional Weapons defines an "incendiary weapon" as "any weapon or munition which is primarily designed to set fire to objects or to cause burn injury to persons through the action of flame, heat, or combination thereof, produced by a chemical reaction of a substance delivered on the target."

The protocol also specifically bans the air delivery of incendiary weapons in densely populated civilian areas.

Syria, however, is not party to the Convention on Conventional Weapons.

A November 2013 Human Rights Watch report condemned Syria's use of incendiary weapons on its civilian population as war crimes, and urged the country to join the CCW.

“Syria has used incendiary weapons to inflict terrible harm on civilians, including many children,” said Bonnie Docherty, senior arms researcher at HRW. 

“Yet where is the international outcry? Other countries should condemn Syria’s use of incendiary weapons just as they have its use of chemical weapons and cluster bombs.”

This footage, compiled by the Guardian, seems to show the aftermath of an attack on Aleppo. Its contents were not independently verified by GlobalPost.

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