A group of nuns held by rebels in Syria for more than three months have been released following Lebanese-Qatari mediation and are on their way to Damascus via Lebanon.

A Lebanese security source said the nuns had been taken to the Lebanese town of Arsal earlier in the week and were headed to Syria on Sunday accompanied by the head of a Lebanese security agency and a Qatari intelligence official.

The British-based Syrian Observatory for Human Rights monitoring group, and a rebel source in the area, said the release of the nuns had been agreed as part of a swap in which the government would free about 150 women prisoners.

The 13 nuns and three maids were kidnapped from the Christian town of Maaloula north of Damascus in December and taken to the nearby Syrian rebel-held town of Yabroud, where they are believed to have been held by al-Qaeda affiliate Jabhat al-Nusra.

Shortly after the nuns disappeared, rebel fighters said they had taken them as their "guests" and that they would release them soon.

In December, the nuns appeared in a video obtained by Al Jazeera, saying they were in good health, but it was not clear under what conditions the video had been filmed.

Syrian state television devoted significant coverage to the release earlier on Sunday, but made no mention of any prisoner exchange agreement. It aired live video from the Lebanese border and interviews with church officials.

A montage of Christian religious imagery including churches, a statue of the Virgin Mary and murals of Jesus was set against dramatic music and described Syria as a "cradle of the monotheistic faiths".

Syria's Christian minority has broadly tried to stay on the sidelines of the three-year-old-conflict, which has killed more than 140,000 people and which has become increasingly sectarian.