Pope Francis called for prayers Wednesday for 12 Orthodox nuns reportedly taken by force from their convent in Syria by rebels. Religious officials in the region have said the women were abducted, but a Syrian opposition activist said they were merely removed for their own safety.

The 12 nuns join two bishops and a priest who are already believed to be held by hard-line rebels, deepening concerns that extremists in the opposition's ranks are targeting Christians. Syria's minorities, including Christians, have largely sided with President Bashar Assad's government or have tried to stay on the sidelines of the country's civil war, fearing for their fate if the rebels, increasingly dominated by Islamic extremists, come to power.

Speaking to a crowd gathered for the pontiff's general audience in St. Peter's Square at the Vatican, Francis invited "everyone to pray for the sisters of the Greek Orthodox monastery of Santa Takla in Maaloula, Syria, who were taken by force by armed men two days ago."

"Let us continue to pray and to work together for peace," he said.

His appeal came as fighting raged in several parts of Syria including the northern city of Aleppo, where rebels firing mortar rounds at government-held neighborhoods killed at least 17 people and wounded dozens more, said Rami Abdurrahman of the Britain-based Syrian Observatory for Human Rights.

Activists also reported clashes in the Qalamoun region north of Damascus, an area that controls the smuggling routes from neighboring Lebanon that help sustain rebel-held enclaves and is also a key transportation corridor from the capital to the central city of Homs.

The region boasts a sizeable Christian population and is home to the ancient Christian village of Maaloula and its Mar Takla convent. Church leaders and pro-rebel activists say the Al Qaeda-affiliated Nusra Front seized the nuns from Mar Takla on Monday.

The rebels took the nuns to the nearby rebel-held town of Yabroud, said Mother Superior Febronia Nabhan, head of the Saidnaya Convent. There was no suggestion that the rebels entered Maaloula specifically to seize the nuns.

Syria's three-year-old conflict began with mostly peaceful demonstrations against Assad's rule but devolved into an armed insurgency after security forces violently cracked down on protesters. Hard-line Sunni Muslim brigades have become increasingly dominant within the rebellion and the conflict has grown ever more sectarian.

A Syrian opposition activist claimed the nuns were taken for their own safety because of heavy clashes nearby. However, rebels would not provide evidence of the nuns' safety, said the activist, who goes by the name Amer.

He said the rebels placed the nuns with a Christian family in Yabroud.

"They are being taken care of," Amer said. His said his information came from friends close to the rebels holding the nuns.

However, a nun in a nearby convent insisted the women were being held against their will.

Stephanie Haddad, deputy of the Greek Orthodox Saidnaya Convent, told The Associated Press that she spoke to the nuns on Tuesday night. She said rebels guarding them in Yabroud kept promising they would be released soon, "but nothing is certain."

Syria's Greek Orthodox Patriarch, John Yazigi, pleaded for the release of the women on Tuesday.

Maaloula was a popular tourist attraction before the conflict began. Some of its residents still speak a version of Aramaic, a language spoken by Jesus.

In another move that underscored the fears of beleaguered minorities, Al Qaeda-linked rebels who control the northern town of Raqqa converted a church into a center for proselytizing their strict interpretation of Islam, and another into an administrative office, said the Observatory's Abdurrahman.

Rebels of the Islamic State in Iraq and the Levant had previously set fires in the two churches and knocked the crosses off them, replacing them with the group's black Islamic banner.

Abdurrahman sent photographs of the Church of Armenian Martyrs, with a black ISIL flag flying from where the cross once stood. Below, a black banner read, "The proselytizing office, region of Raqqa."