"Please help us - the bombs are falling all around us, but we are not going to leave the people in their suffering," said Sister Anne-Françoise of Aleppo's Discalced Carmelite Sisters.
The Syrian government has cut off all supplies into Aleppo as it attempts to take back the city from rebels.
More than 250,000 civilians have been under siege in the city since the middle of July.
Despite the desperate conditions Sister Anne-Françoise says her convent is there to stay.
"When the Syrian army attempts to prevent the opposition and other groups from entering into the city, the bombing and shelling is really close to us," she told Aid to the Church in Need.
"Thanks be to God, they haven't hit us yet, but we are constantly hearing the shells pass over our heads."
A number of refugee families are living at the convent, said Sister Anne-Françoise.
"By now it is only the poorest of the people who are still left here in Aleppo. So many Christians have left the city during these years of war.
"We have no water, no electricity, and the fighting is continuing incessantly. Who could possibly come back in these conditions?
"The Middle East, the land of Christ, now risks becoming empty of Christians. That is unthinkable, and yet the situation is truly terrible.
"And even for those who leave, the crisis does not end. They find themselves uprooted from their own soil and sometimes even lose their spiritual roots as well.
"How can we abandon these people in their suffering? The witness of our presence is important for them.
"We draw strength and courage from prayer - this is our protection. The diplomatic solutions have not worked. We simply pray to the Lord that this war may stop."
In a message issued at the end of last month, Melkite Greek-Catholic Archbishop Jean-Clement Jeanbart of Aleppo described the situation for those remaining in the city.
He wrote: "The increase of unprecedented and indiscriminate bombing has terrorised those in the residential areas of the city, and has caused considerable losses to the businesses of our faithful - all of this has sewn fear and disarray in their hearts, and has terrified the women and children."