Reuters reports: [D]iplomats and rebels interviewed by Reuters said Assad’s generals had been trying for some time to push the rebel units back to the southern ring road that separates Damascus from its more rural environs and neutralise the immediate threat to the heart of the capital.

The suburbs of Zamalka, Jobar and Ain Tarma sit in an expanse of farming country known as the Eastern Ghouta. Along with the town of Mouadmiya in the west, these areas had been pummelled for months by battlefield artillery, warplanes and surface-to-surface missiles before they were hit on the morning of Aug. 21.

In the 72 hours that followed, Assad’s mechanised forces from the Fourth Division and the Republican Guards, the praetorian units entrusted with defending his seat of power, mounted a major push to retake the four areas, but well dug-in rebels held out, sources said.

“The regime has been throwing everything he has at the Ghouta, but it remained a thorn in its side. When you have a large number of well-organised rebel fighters in an urban area with lots of cover, using chemical weapons becomes very tempting,” a Middle East based diplomat said.

When the revolt became militarised almost two year ago, the rebels of Ghouta, mostly from the Sunni majority that opposes Assad and his minority Alawite sect elite, were among the first areas in the country to take up arms.

The rebel groups there include the Saudi-backed Liwa al-Islam Brigade, Saladin Brigade, Jobar Martyrs Brigade, and Tahrir al-Sham, a unit headed by Firas al-Bitar, an officer who defected from Assad’s army and has a reputation as a good military planner.

“If the rebel units were not so well organised, Assad would have captured Ghouta long time ago,” said Moaz al-Shami, a prominent activist who witnessed fighting in Ghouta.

“The regime needed to kill 1,000 people in one go in Ghouta, or whatever the final tally of the chemical attack proves to be, because it was in need of a morale boost,” he added.

In the last few weeks, rebel brigades based in Jobar, which is only three kilometres from the central Abbassiyeen Square, managed to open a supply corridor to the besieged Damascus neighbourhoods of Barzeh and Qaboun in the northern sector of the capital, opposition sources said.

The link brought the military threat from Ghouta closer to the heart of Damascus and helped the two districts withstand intensifying loyalist attacks, the sources said.

“Rebel operations in the countryside have been merging with Damascus, and the regime could not take that. Assad would have loved to gas Barzeh and Qaboun as well, but they are too interconnected with loyalist areas,” said Khaled Omar, a member of the opposition Local Council of Ain Tarma.

“By hitting Ghouta, Assad thinks he is preserving Damascus and destroying a popular incubator of the revolution,” he added.