Over a thousand children have been killed in indiscriminate air attacks carried out by the Syrian government since the civil war broke out in March 2011, a human rights organisation revealed.

A report by the Syrian Observatory for Human Rights pointed to the continuing use by the Syrian air force of so-called barrel bombs as one of the reasons for the high casualty figures.

A barrel bomb is a type of improvised explosive device used by the Syrian air force. These bombs are typically made from barrels that have been filled with high explosives combined with shrapnel and then dropped from helicopters.

Overall, nearly 5,000 civilians have lost their lives in the attacks by Syrian warplanes and helicopters, according to the human rights watch group.

Women have not been spared as well from the air strikes as the total number of casualties included nearly a thousand women, the group said.

About 26,000 other civilians have been injured in the attacks while dozens of thousands have been forced to flee their homes to find a refuge from the air strikes.

Public and private properties have also been destroyed while others have been heavily damaged, the group said.

The Syrian air force carried out 26,517 air strikes from Oct. 20 last year up to July 21 this year, the group said. Helicopters dropped more than 14,000 barrel bombs in the provinces of Rif Dimashq, Aleppo, Homs, Hama, al- Hasakah, Deir Ezzor, al- Quneitera, al- Suwaydaa, Daraa, Idlib and Lattakia, it said.

Warplanes carried out more than 12,000 raids in Damascus, Rif Dimashq, Aleppo, Homs, Hama, al- Hasakah, Deir Ezzor, al- Raqqa, al- Quneitera, Daraa, al- Suwaydaa, Idlib and Lattakia, the rights watch body added.

The forces of Syrian President Bashar al-Assad, backed by close to 3,000 Hezbollah soldiers, have been seeking to recapture lost territories near the border with Lebanon. Rebel forces, which include the al-Qaeda affiliated groups of Jabhat al-Nusra and Ahrar al-Sham, have retaliated by firing rockets and heavy mortar shells on several villages.

Meanwhile, the United Nations Special Envoy for Syria, Staffan de Mistura, has expressed concern over the civilians affected by the large number of barrel bombs dropped in the north-western city of Zabadani in Syria, saying "civilians are tragically caught in the middle of the fighting."

De Mistura said the bombs have caused "unprecedented levels of destruction and many deaths among the civilian population," in the town near the border between Syria and Lebanon.

Armed opposition forces who call themselves the "Army of Conquest" hit back by firing rockets and heavy mortar shells on two villages near Idlib, Al Foua and Kefraya, where a large number of civilians are trapped.

The UN special envoy also called on all parties to protect civilians and for the Syrian government "to halt the use of crude and indiscriminate weapons, such as barrel bombs, on its own cities."