Civilians killed in relentless regime bombing of besieged Damascus suburb

Six days of heavy bombing have killed dozens in the region, where rebel groups and regime forces are locked in a cycle of tit-for-tat attacks.

Government forces have escalated their bombardment of Eastern Ghouta, an opposition stronghold outside Damascus, since hardline rebel group Ahrar al-Sham attacked a military base in the area last week.

Since Tuesday, heavy artillery fire and air strikes on Eastern Ghouta have killed at least 66 civilians including 13 children, according to the Syrian Observatory for Human Rights, as well as three rescue workers from the Syrian Civil Defence - better known as the White Helmets.

At least 281 people have been wounded, the Britain-based monitor said on Sunday.

Rebel groups meanwhile have fired rockets into Damascus neighbourhoods, killing at least 16 people since Thursday, the Observatory said.

The toll included two people killed by rocket fire on Sunday.

Eastern Ghouta is supposed to be part of a "de-escalation zone" under a deal between Russia, Iran and Turkey aimed at reducing the level of violence.

President Bashar al-Assad's forces have besieged Eastern Ghouta since 2013, making humanitarian conditions in the area, where some 400,000 people live, extremely dire.

On Sunday, the UN's coordinator for humanitarian and development affairs in Syria, Ali al-Zaatari, called on "all warring sides to avoid targeting civilians".

"For days, there have been daily reports about civilians being killed and others being severely wounded, in addition to warehouses, hospitals and schools being put out of service during the exchange of shellfire, particularly in Damascus and Eastern Ghouta," Zaatari said.

The Syrian conflict began when the Baath regime, in power since 1963 and led by Assad, responded with military force to peaceful protests demanding democratic reforms during the Arab Spring wave of uprisings, triggering an armed rebellion fueled by mass defections from the Syrian army.

The brutal tactics pursued mainly by the regime, which have included the use of chemical weapons, sieges, mass executions and torture against civilians have led to war crimes investigations.