At least four civilians were killed and six others injured on Tuesday when Assad regime forces struck a Syrian city that falls within a network of “de-escalation zones”, according to a pro-opposition Syrian civil defense official.

Axar.az reports that regime forces fired 12 “Elephant missiles” at the opposition-held Ain Tarma district of Eastern Ghouta, which is located inside a de-escalation zone, Mahmoud Ethem, a member of Syria’s White Helmet civil defense forces told.

“At least four civilians were killed and six others injured, while several homes were damaged in an attack on residential parts of the city,” Ethem said.

For the last five years, Eastern Ghouta has remained under siege by the Assad regime.

During peace talks held in Astana in early May, Eastern Ghouta was designated as part of a network of de-escalation zones in which acts of aggression would be expressly forbidden.

A first round of peace talks was held in the Kazakh capital on Jan. 23 and 24 after a ceasefire was hammered out on Dec. 30.

The Astana talks are being brokered by Turkey, which backs the Syrian opposition, along with Russia and Iran, both of which support the Assad regime.

Syria has been locked in a vicious civil war since early 2011, when the Assad regime cracked down on pro-democracy protests with unexpected ferocity.

Since then, hundreds of thousands of people have been killed and more than 10 million displaced, according to UN officials.

Assad regime officials, however, put the conflict’s total death toll much lower.