United Nations Special Envoy for Syria Staffan de Mistura said he is “appalled and shocked by the high number of rockets indiscriminately launched by armed opposition groups” that killed scores of civilians in Aleppo over the last 48 hours, a statement released by de Mistura’s office says.

Scores of civilians, including several children, were killed while hundreds of others were wounded in “relentless and indiscriminate” attacks carried out by opposition groups in the western districts of Aleppo, according to the UN statement.

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“Those who argue that this is meant to relieve the siege of eastern Aleppo should be reminded that nothing justifies the use of disproportionate, indiscriminate [attacks,] including heavy weapons on civilian areas and it could amount to war crimes,” de Mistura said.

He echoed the condemnation voiced by the UN secretary-general regarding the attacks on schools. The special envoy also criticized the “use of heavy airpower on civilian areas.”

“The civilians of both sides of Aleppo have suffered enough due to futile but lethal attempts of subduing the city of Aleppo,” he said. “They now need and deserve a stable ceasefire covering this ancient city of Syria.”

Earlier on Sunday, state news agency SANA reported that “shells containing poison gases” had been fired at the residential district of al-Hamdaniya in western, government-held Aleppo.

RT Arabic's crew in Aleppo reported 36 cases of suffocation. Al-Mayadeen reported that all the victims of the attack are civilians.

Just recently, the Russian Defense Ministry reported on a number of attacks in Aleppo that targeted schools and claimed the lives of at least three children in the period of 24 hours. Twelve more people died in an attack on a humanitarian aid corridor opened next to a school in the Al-Mashariq district, according to the ministry’s information. Twelve more people were injured.

READ MORE: Over 16,000 Syrians killed by US-backed rebels since February – Russian UN mission

Meanwhile, according to Russia's Permanent Mission to the United Nations, over 16,000 people have fallen victim to opposition groups meant to be under US control. “From February to September, the opposition groups that are supposed to be under the US control committed 2,031 violations of the [cessation of hostilities], which claimed lives of 3,532 military personnel and 12,800 civilians,” the Mission’s statement, published on the website of the Russian Foreign Ministry, reads.

According to Dr. Said Sadek, professor of Political Sociology at the American University of Cairo, it’s not likely that Western powers and the Gulf states will end their backing for rebel groups, even if they are found responsible for using chemical weapons in Aleppo.

“We have to understand that for six years, the Western countries and the Gulf states invested in those ‘moderate’ or radical groups, and so they cannot abandon them,” Sadek explained. “They cannot pull out now and say, ‘OK we discovered that we are wrong, let’s get out and leave them.’ They have invested in them and they will still use them for bargaining in the future of Syria.”

Despite the UN envoy’s condemnation, a real shift in the attitude towards “moderate” groups shelling western Aleppo with chemical munitions in highly unlikely, according to former US diplomat Jim Jatras. He believes public opinion in the West won’t change, since “continuous attacks against west Aleppo… received zero report” in the mainstream media while the governments put “roadblocks” on any impartial investigation into such matters.

“You would not know from the American mainstream media that we’re supporting terrorists in east Aleppo, that was Al-Qaeda and other groups,” Jatras told RT. “These are groups supported by the US and other Western countries and by our allies in the region – Saudi Arabia, Qatar and so forth – despite the fact that these are terrorists groups, that they are Al-Qaeda and their various allies. And they are very reluctant to put a spotlight on the kind of people that we’re supporting in this region. Let’s remember, a couple of month ago the al-Zinki group was alleged of using chlorine gas, just like we’ve seen today. And the State Department spokesman was asked if we were shown [that] they used chlorine gas, would we drop our support for them? And he refused to answer. So I’m afraid we’re going to see a roadblock put in by Western governments to avoid that kind of investigation.”