(CNN) -- Pope Francis Wednesday urged people to pray for 12 nuns abducted from a Greek Orthodox monastery in Syria.
"Let us pray for these sisters, and for all those who have been kidnapped on account of the ongoing conflict. Let us continue to pray and to work for peace," the Pope said. He ended his appeal by saying that all should have confidence in the Virgin Mary, calling her a "Queen of Peace."
Three girls who grew up at the convent were kidnapped along with the nuns, an Orthodox official said Thursday.
A woman identifying herself as the mother superior of nearby Saidnaya Greek Orthodox convent said a caller phoned after they were first taken just to say that they were safe.
Syrian state media SANA reported that "armed terrorists" took the nuns, implying that rebels fighting to oust President Bashar al-Assad are behind the attack.
The chief of an opposition group based in London told CNN he had confirmed that al-Nusra Front fighters took the nuns, but Rami Abdurrahman said the fighters did so to protect them from what the group believed would be an impending attack by Syrian government forces.
Abdurrahman leads the Syrian Observatory for Human Rights.
The U.S. State Department has designated the al-Nusra Front a terrorist organization with links to al Qaeda.
CNN could not confirm Abdurrahman's account of what happened to the nuns.
The Observatory wants the Red Cross to intervene for the nuns' release, he told CNN.
The nuns' abduction is just the latest trauma in the civil war in Syria that has raged since March 2011. The United Nations says more than 100,000 Syrians have been killed and 9 million people have been displaced.
The Monastery of Saint Tecla is in the predominantly Christian village of Maalula, about 40 miles west of Damascus. Reports say rebels were behind Saturday's abduction.
The incident at the monastery underscores the fear some have that Christians are being targeted in an already complex conflict that has involved numerous players.
Meanwhile, at least 17 people were killed and 30 others were injured Wednesday in mortar or rocket attacks in the northern Syrian city of Aleppo, one of the long-contested battlegrounds of the country's civil war, state-run media and an opposition group said.
Opposition activists fighting against the government of Syria say 17 people were killed, but the government says 18 people died.
The Syrian Observatory for Human Rights said the attack in Aleppo hit at least one neighborhood known to favor al-Assad. Details on who launched the attack were not immediately available.
At least seven of the injured were in critical condition Wednesday, the opposition group said. Among the dead were nine civilians and five members of the government's forces, according to the group.
Aleppo city and Aleppo province have, for many months, been a battleground between government forces and opposition fighters of different groups, including the al Qaeda-linked Islamic State in Iraq and the Levant, and the more moderate Free Syrian Army.
Syria plans to send a delegation to Switzerland early next year to participate in peace talks, but it's not clear which opposition groups will attend. The United Nations announced that the Geneva II conference aimed at ending the Syrian civil war starts January 22.
Geneva II is a successor to Geneva I, a June 2012 meeting in which international parties laid out a peace plan for Syria that calls for a transitional governing body. It left open the question of whether al-Assad must leave office.
The United States and Russia announced in May that they would try to bring the warring parties to a second conference in Geneva to implement the plan. But the second Geneva conference has been delayed several times.
International inspectors, meanwhile, are trying to ensure that the Syrian regime eliminates its chemical weapons stockpile by the middle of 2014. Syria agreed to do so under international pressure earlier this year over allegations the Syrian government used sarin nerve gas in an August 21 attack on a Damascus suburb. U.S. officials said at least 1,400 people died in the attack. Syria denied responsibility, blaming rebel forces.