At least 250 civilians were reportedly killed there within the last three days.
"We call on the Arab and Islam countries and international community to take imminent actions to stop mass killings and save the innocent civilians in eastern Ghouta," according to a statement issued by the IUMS.
The IUMS condemned the “massacre of Assad Regime backed by Russia with weapons against which the [Syrian] people cannot counter.”
Since Tuesday, regime forces have stepped up attacks on Eastern Ghouta using barrel bombs, artillery fire and other types of weapons, according to an Anadolu Agency correspondent based in the area.
Over a three-day period, the regime has reportedly carried out 260 separate attacks in Eastern Ghouta, killing more than 250 civilian residents of the district.
At peace talks held in the Kazakh capital Astana in May of last year, Turkey, Russia and Iran designated Eastern Ghouta as a “de-escalation zone” in which acts of aggression would be expressly prohibited.
Nevertheless, Russia -- one of the agreement’s three guarantor-states -- has failed to prevent the Assad regime from repeatedly violating the terms of the truce.
Home to some 400,000 civilian residents, Eastern Ghouta has remained under a crippling regime siege for the last five years, which has brought the district to the verge of a humanitarian catastrophe.
Syria has been locked in a devastating conflict since early 2011 when the Assad regime cracked down on demonstrators with unexpected ferocity.
According to UN officials, hundreds of thousands of people have been killed in the conflict to date.