Sister Annie Demerjian, a member of the Sisters of Jesus and Mary, has asked why Western journalists are looking mainly at casualties in areas of the country held by rebels, but not at the victims in government-controlled areas.
Speaking to Catholic News Service, she said: "It is not fair."
The conflict has been ongoing for six years between forces loyal to President Bashar al-Assad and rebel groups, including the terror group Islamic State.
Sister Annie Demerjian went on: "We don't see a balance.
"Last week nobody spoke about a (Christian) woman who pulled her son from a balcony without his head, and just a river of blood coming out of his neck."
She told the news service he had been hit by a shell.
"There are many stories like that.
"It is very painful when shells are falling in residential areas. Many people die," she said.
Sister Annie went on: "Why is the world silent about it? People don't know what is happening."
She said that Christians and Muslims lived peacefully side-by-side before the war.
"We didn't have divisions between Muslims and Christians before. This is new," she said.
Pope Francis says he is begging for an immediate ceasefire in Syria.
In his weekly general audience he said that he wants "at least" a truce to allow civilians, especially children, to be evacuated from Aleppo.
Russian jets have resumed bombing the city, ending days of relative calm there.
Millions have been displaced by the conflict so far.
