Shelling of rebel bastion near Syrian capital kills 19

At least 19 civilians were killed in heavy aerial bombardment of several opposition-held towns east of the Syrian capital on Tuesday, a monitoring group said. 

Six children were among the dead in Eastern Ghouta, the largest rebel bastion near Damascus, the Syrian Observatory for Human Rights confirmed.

"It was a series of airstrikes throughout the day and the death toll may still rise," the Britain-based group added.

Civilians had died in Jisreen, Kafr Batna and the largest of the towns in Eastern Ghouta, Douma.

Half a dozen wounded children were seen sitting on the floor of a makeshift clinic, caked in dust and blood as they awaited treatment, an AFP photographer in Douma reported.

Fourteen of the victims died in airstrikes on an area between the opposition-held towns of Hammuriyah and Saqba.

Another AFP photographer in Saqba reportedly saw residents scrambling over rubble and through clouds of dust, tossing debris aside as they searched for signs of life. 

The Observatory said Tuesday's bombardment brought to 49 the number killed in Eastern Ghouta in two days of attacks.

"There has been fierce artillery shelling and airstrikes since yesterday, and 165 people total have been wounded," Observatory chief Rami Abdel Rahman said.

Eastern Ghouta has been under a devastating government siege since 2012, and is targeted regularly by air strikes and artillery.

It is the last remaining opposition stronghold near Damascus, where a string of local "reconciliation deals" have seen villages and towns brought back under the control of President Bashar al-Assad's government.

Hundreds of people were killed in Eastern Ghouta in chemical weapons strikes allegedly carried out by government troops in August 2013.

On Tuesday, at least 58 people were killed in a suspected chemical attack on the northwestern Syrian town of Khan Sheikhun, according to the Observatory.

Dozens more suffered respiratory problems and symptoms including vomiting, fainting and foaming at the mouth, the monitor and doctors at the scene said.

More than 320,000 people have been killed and millions displaced since Syria's war started in 2011 with the brutal repression of anti-government protests.