Human Rights Watch has echoed accusations by Syrian activists that Russia was behind the use of new advanced cluster munitions in Syria, by dropping them from its warplanes or supplying them to the Assad government.
The New York-based group said that photographs it obtained showed that the cluster munitions were dropped on Kafr Halab, a village southwest of Syria's second city of Aleppo, on October 4.
"It's disturbing that yet another type of cluster munition is being used in Syria given the harm they cause to civilians for years to come," said Nadim Houry, Human Rights Watch's deputy Middle East director.
"Neither Russia nor Syria should use cluster munitions, and both should join the international ban without delay."
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Russia launched an aerial bombing campaign against opponents of President Bashar al-Assad on September 30.
Cluster munitions contain dozens or hundreds of bomblets and are fired in rockets or dropped from the air.
Widely banned, they spread explosives over large areas and are indiscriminate in nature, often continuing to maim and kill long after the initial attack when previously unexploded bomblets detonate.
Their use in Kafr Halab coincides with the emergence of evidence that they have been used in the provinces of Aleppo, Hama and Idlib since Russia launched its intervention.
Human Rights Watch said it "cannot conclusively determine whether Russian or Syrian forces were responsible for the attack" on October 4.
It noted that neither country had banned their use.
A video posted on October 7 by activists that was reportedly taken in the town of Kafr Zeita, northwest of Hama, shows smoke trails of ground-fired rockets launched from the direction of Jabal Zayn al-Abidin and multiple subsequent explosions of submunitions in the town.
Photographs and a video posted online by local activists in October, with title text that says they were taken at Masaran village in Idlib, shows at least one unexploded AO-2.5RT submunition and the remnants of an RBK-500 canister, which can contain up to 108 submunitions.
Reuters published a photograph taken in Masaran that shows a first responder handling unexploded AO-2.5RT submunitions that local activists told the news agency were used in an attack by the Russian air force on October 7.
Human Rights Watch has documented the use of cluster munitions before in the Syrian conflict, with government forces dropping them from the air since 2012, and the Islamic State of Iraq and the Levant (ISIL) group firing them from rockets since late 2014.
According to RT television network, Russia is using in Syria "time-proven bombs and missiles equipped with state-of-the-art system guidance. Precision weapons are used from high altitudes to exclude encounters with portable air-defence systems".
Russian President Vladimir Putin told local media that Russia has the will to use these advanced weapons "if it meets the national interests of our state and the Russian people".
The Syrian conflict, which began as an uprising against Assad's government in 2011, has killed up to 250,000 people and forced millions to flee the country.
Source: Al Jazeera and agencies