Activists and rescue teams have accused the Syrian government of launching an attack with suspected poisonous gas that has affected nearly 20 civilians in a rebel-held suburb near the capital, Damascus.

The team of emergency workers known as While Helmets, or Syrian Civil Defence, says the attack hit a neighbourhood in the Douma district early on Monday.

It says the rescuers evacuated more than 20 civilians, most of them women and children from the area, which they say was hit with suspected chlorine attack.

The Ghouta Media Centre, an activist-operated media, also claims the attack involved chlorine gas. Activists say a foul smell followed a series of bombings that hit the Douma neighbourhood.

Such claims are not new but they are difficult to verify because of lack of chemical labs and independent testers. A UN inquiry panel had previously blamed the government for a number of chlorine and sarin attacks in Syria.

The Easter Ghouta suburb of Damascus has been under intensive attack, and the UN says government forces are holding 400,000 people under siege there.

The United States accused Russia of “costing innocent Syrian lives”, following the reported attack.

US State Department spokeswoman Heather Nauert said Moscow’s “unwillingness or inability to restrain the (Bashar) Assad regime is costing innocent Syrian lives”.

She said the United States has tried to hold responsible those using chemical weapons in attacks that “have killed far too many Syrians”.