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The death toll included 58 children and 42 women, the group said in what was termed as the deadliest attack in the city in the last few years.
The SOHR activists and residents described it as "being under constant bombardment". The rights group said at least 106 of the civilian deaths took place on Tuesday.
The monitoring group said the death toll is the highest since the 2013 alleged chemical attack on Eastern Ghouta, which activists say killed approximately 1,400 people.
"These are the worst days of our lives in Ghouta," Eastern Ghouta hospital director and pediatrician Amani Ballour said. "We in Ghouta have been getting hit by air strikes for more than five years and this is not new to us ... but we have never seen anything like this escalation."
Various Islamic rebel groups control Eastern Ghouta, including the Al Qaeda-linked Hayat Tahrir al-Sham, which was previously known as Jabhat al Nusra before renouncing its ties to Al Qaeda.
Medical supplies were already in short after years-long siege of the area that began in 2012.
Now, Syrian regime forces are accelerating their offensive against the suburb, one of the last rebel-controlled areas in the country.
"I can tell you that the situation is very catastrophic ... there were four hospitals that were destroyed...," said Fares Ouraiba, a doctor from the Damascus suburb. He said most of the dead were women and children.
Besides, 13 more people were killed and 77 others wounded when militants in Eastern Ghouta fired 114 rocket and mortar rounds on several neighbourhoods here on Tuesday, said Syria state-run SANA news, citing police.
SANA added that the Syrian army responded to the attacks with "precise strikes", destroying rocket launchers and fortified positions used by the armed groups.