LONDON  - More than 11,000 children have died in Syria’s civil war, including 128 killed by chemical weapons in a notorious attack and hundreds targeted by snipers, a British think-tank said Sunday.

The Oxford Research Group, which specialises in global security, said in a new study that there were 11,420 recorded deaths of children aged 17 years and under. The report, entitled “Stolen Futures: The hidden toll of child casualties in Syria”, analyses data from the beginning of the conflict in March 2011 until August 2013.

The think-tank added that, of the 10,586 children whose cause of death was recorded, 128 were killed by chemical weapons in Ghouta, near Damascus, on August 21,2013, in an attack that the United States and other world powers blamed on President Bashar al-Assad’s regime.

Syria has since agreed to destroy its entire chemical weapons arsenal as part of a deal to head off US military strikes.

The think-tank added on Sunday that 764 children were summarily executed and 389 were killed by sniper fire in the conflict. Explosive weapons have caused more than 70 percent of the child deaths, while small arms fire accounts for more than a quarter, according to the study.

“What is most disturbing about the findings of this report is not only the sheer numbers of children killed in this conflict, but the way they are being killed,” said report co-author Hamit Dardagan.

“Bombed in their homes, in their communities, during day-to-day activities such as waiting in bread lines or attending school; shot by bullets in crossfire, targeted by snipers, summarily executed, even gassed and tortured.

“All conflict parties need to take responsibility for the protection of children, and ultimately find a peaceful solution for the war itself.”

Meanwhile, at least 160 rebel fighters and Syrian troops have been killed in two days of clashes in the Eastern Ghouta region just outside Damascus, a monitoring group said on Sunday. The latest fighting comes against the backdrop of regime advances in Damascus province that have cut rebel supply lines to the capital and its southern districts.

The Syrian Observatory for Human Rights said the fighting began Friday when rebel forces, including jihadist fighters, launched attacks against checkpoints and military stations in five areas in the Ghouta region.

“They are trying to break the siege imposed by the army on the region,” Observatory director Rami Abdel Rahman told AFP.

The group said the dead included 55 rebel fighters, including seven battalion leaders, and 41 jihadists from the Al-Qaeda-affiliated Islamic State of Iraq and the Levant and the Al-Nusra Front.

At least 36 Syrian regime troops were also killed, along with 20 members of a Shiite Iraqi group fighting alongside the army, and eight members of a Syrian pro-regime militia.

The Observatory said the Lebanese Shiite group Hezbollah was also fighting alongside the Syrian army, but gave no details on casualties in its ranks.

The group, which relies on a network of activists, doctors and lawyers on the ground, also said five citizen journalists, including three who had fought alongside the rebels, were killed in the fighting.

Eastern Ghouta, a ring of suburbs besieged by the army for months, was one of the areas targeted in an August chemical attack that the US and other world powers blamed on President Bashar al-Assad’s regime.

As part of a deal to head off US military strikes, Damascus has agreed to destroy its entire chemical weapons arsenal.

Syria is cooperating with the disarmament operation being carried out by international experts, who have reported that the entire chemical arsenal has been sealed, awaiting destruction.

But despite the deal, Ghouta has remained under a tight siege and subjected to continued shelling by regime troops, with activists warning of a humanitarian disaster in the rebel stronghold.

In recent weeks, the Syrian army has recaptured a string of areas south of Damascus, turning its attention to both Ghouta and the strategic Qalamoun region north of the capital.

On Tuesday, the army captured Qara, a town on Qalamoun close to the Lebanese border.

It hopes to further disrupt rebel supply lines to areas around the capital by cutting access to the Lebanese border, which food, weapons and fighters regularly cross.

The Syrian conflict, which began in March 2011, has killed more than 120,000 people and prompted millions to flee their homes.