Assad regime warplanes on Tuesday struck the city of Douma east of capital Damascus, which lies within one of several so-called de-escalation zones, according to a pro-opposition Syrian civil defense official.

Speaking to Anadolu Agency, Firas al-Halli of Syria's White Helmet civil defense forces said regime warplanes had targeted a residential part of the city.

According to al-Halli, one woman and one child were killed in the attack, while an unspecified number of other civilians were injured.

For the last five years, Douma -- home to some 200,000 people -- has remained under siege by foreign terrorist groups allied with the Assad regime.

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

On Tuesday, a fifth round of peace talks kicked off in the Kazakh capital.

A first round of peace talks was held in Astana on Jan. 23 and 24 after a ceasefire was reached 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 regime cracked down on pro-democracy protests with unexpected ferocity.

Since then, hundreds of thousands of people have been killed in the conflict and more than 10 million displaced, according to U.N. officials.