Health officials in the rebel-held enclave of Eastern Ghouta are accusing Syrian government forces of using chlorine gas in their aerial bombardment campaign in the Damascus suburb.

Syria's Civil Defense, also known as the White Helmets, said on Sunday that at least one child died as a result of suffocation on their official Twitter account.

According to the Syrian opposition's interim government, victims were showing symptoms "consistent with exposure to toxic chlorine gas".

The opposition's health ministry said in a statement that several people were admitted to medical facilities in nearby Al-Shifoniyah.

Symptoms include "dyspnea, intensive irritation of the mucus membrane, irritation of the eyes and dizziness", the ministry said.

At least 18 people were treated with oxygen nebulising sessions, the statement added.

Several women and children were experiencing difficulty breathing, according to the White Helmets.

The reports of the gas attack come as President Bashar al-Assad's forces fight against opposition groups from multiple fronts, in an attempt to penetrate into the besieged enclave.

'Front lines'

Eastern Ghouta has been under rebel control since 2013. Since, the Syrian government has imposed a siege on the suburb in an attempt to drive them out.

Al Jazeera's Zeina Khodr, reporting from Beirut in neighbouring Lebanon, said Al-Shifoniyah is a target as the "pro government alliance" are trying to hit areas in Eastern Ghouta close to the front lines.

"What the pro-government alliance is trying to do is target these areas on the edges of Ghouta to make it easier for their ground forces to push and advance," she said.

"The government has not been able to take any inch of territory in Ghouta since the ground offensive began on Sunday," she added.

The government's continuous shelling has killed at least 16 civilians since Monday morning in one of Eastern Ghouta's main towns, Douma, a local activist told Al Jazeera.

According to Alaa al-Ahmed, 10 of those who lost their lives on Monday were from the same family.

At least 27 people were killed on Sunday as a result of shelling by Russian-backed Syrian warplanes, which have been targeting various "districts and towns" across the Damascus suburb, according to Al Jazeera's Mohammed Al Jazaeri, reporting from Eastern Ghouta.

The attacks come after the UN Security Council voted unanimously in favour of a resolution on Sunday, calling for a 30-day ceasefire in Syria.

Last week, deadly air strikes and artillery fire launched by Russian-backed Syrian forces exacerbated a dire humanitarian crisis in the besieged enclave, home to some 400,000 people.

According to the Syrian Observatory for Human Rights (SOHR), more than 500 civilians lost their lives as a result of the aerial bombardment campaign that began on February 18.

Earlier this week, the UN and other international bodies expressed outrage at the number of civilian casualties.

Hundreds of thousands of people have died in fighting during Syria's seven-year civil war, and millions have been forced to flee the country.