Data compiled by Human Rights Watch shows an important increase in the use of cluster bombs in the past two weeks in Syria. The cluster bombs strikes are part of an intensifying air campaign by government forces on rebel-held areas that has included dropping high explosive, fragmentation, and even improvised “barrel” bombs into populated areas.

Syria’s army denies using cluster bombs; however, Human Rights Watch has gathered new evidence of ongoing cluster bomb attacks by Syria’s air force and has confirmed them through interviews with victims, residents and activists who filmed the cluster munitions.

“Syria’s denial is meaningless as evidence mounts that cluster bombs are raining down on towns and villages,” said Steve Goose, arms director at Human Rights Watch. “Syria’s air force is imposing a reign of terror on civilians in rebel-held areas across the country with cluster bombs and other explosive weapons dropped from aircraft.”

Human Rights Watch has received information about more than 35 cluster bomb strike sites. Videos and photos of cluster bomb’s remnants indicate that the Syrian air force has used at least 46 cluster bombs. At least 136 unexploded bomblets from the attacks have been identified, all of which pose grave dangers to civilians.

Two cluster bomb victims in the town of Eastern al-Buwayda, as well as residents in the towns of Rastan, Talbiseh, al-Bab, and Qusayr, witnessed cluster bomb air strikes and filmed the aftermath so to directly provide the footage or photos to Human Rights Watch.

The 64 videos reviewed were posted on YouTube in October. In each video, Human Rights Watch experts identified cluster bombs containing explosive bomblets (also called submunitions) that apparently had been dropped by aircraft, including helicopters. Two types of RBK cluster bombs have been identified, one containing 150 AO-1SCh antipersonnel fragmentation bomblets and one containing 30 PTAB-2.5M anti-armor bomblets. In most of the reviewed videos, the visible physical damage to the bombs and the submunitions show them to have been air-delivered.

A review of the markings on the bombs and the submunitions contained inside them, as well as a comparison with the Soviet manuals for the weapons, shows that they were manufactured in the 1970s and early 1980s at Soviet state munitions factories. The most numerous submunitions identified are AO-1SCh antipersonnel fragmentation bomblets, and all appear to have been manufactured at a Soviet factory corresponding to the marking code of 55.

On October 15, the Russian foreign minister, Sergey Lavrov, denied the use of “Russian-made” cluster bombs in Syria. He said there was “no confirmation” of use and said it is very “difficult” to establish where the cluster munitions came from.

It is not publicly known how Syria acquired RBK cluster bombs, it is known that these cluster bombs were exported by the former Soviet Union in significant quantities. Authoritative publishers of specialist military hardware handbooks like IHS Jane’s, as well as materials published by the Russian military-industrial complex, state that RBK series cluster bombs were marketed by the Bazalt State Research and Production Enterprise in Moscow.

“While Foreign Minister Lavrov may justify his denial when it comes to modern ‘Russian-made’ cluster bombs, all the evidence so far shows that the weapons being dropped by Syrian government helicopters and jet aircraft originated in the Soviet Union,” Goose said.

In recent days several governments have condemned Syrian use of cluster bombs, including Austria, Belgium, Denmark, France, Germany, Norway, and Qatar.