BEIRUT — The Islamic State group (ISIS) released at least 19 Christians on Sunday who were among the more than 220 people the militants took captive in northeastern Syria last week, activists and a local leader said.

The news provided a modicum of relief to a Christian Assyrian community that has been devastated by the abductions, which saw ISIS fighters haul off entire families from a string of villages along the Khabur River in Hassakeh province. But fears remain over the fate of the hundreds still held captive.

Bashir Saedi, a senior official in the Assyrian Democratic Organization, said the 16 men and three women arrived safely Sunday at the Church of the Virgin Mary in the city of Hassakeh. He said the 19 — all of them from the village of Tal Ghoran — had traveled by bus from the ISIS-held town of Shaddadeh south of Hassakeh.

The Assyrian Human Rights Network also reported the release, and published photographs on its Facebook page that it said were from Hassakeh showing a crowd dressed in winter coats greeting the returnees.

The photos appeared genuine and corresponded to Associated Press reporting.

It was not immediately clear why ISIS freed these captives.

Saedi said all those released were around 50 years of age or older, which suggests age might have been a factor. The Assyrian Human Rights Network, meanwhile, said the captives had been ordered released by a Shariah court after paying an unspecified amount of money levied as a tax on non-Muslims.

The Britain-based Syrian Observatory for Human Rights also said a Shariah court had ruled the captives be freed, but the reasoning behind the decision was unknown.

The fate of the more than 200 other Christian Assyrians still in ISIS' hands remains unclear. Most of them are believed to have been taken by Islamic State fighters to Shaddadeh, which is located 50 kilometers (30 miles) south of Hassakeh.

Assyrian leaders and Sunni tribal sheikhs have begun reaching out to ISIS to try to negotiate the release of the captives, activists said.

"We're trying to contact any party that might help. We're working through our friends the tribal sheikhs," said Younan Talia, a senior official in the Assyrian Democratic Organization. "Some friends of Daesh are trying to send messages."

Talia said there has been no response yet. Daesh is an Arabic acronym for ISIS.

The Sweden-based director of the Assyrian Network for Human Rights in Syria, Osama Edward, also said efforts were underway to try to negotiate the captives' release.

The abductions have added to fears among religious minorities in both Syria and Iraq, who have been repeatedly targeted by ISIS. During the militants' bloody campaign in both countries, where they have declared a self-styled caliphate, minorities have been repeatedly targeted and killed, driven from their homes, had their women enslaved and places of worship destroyed.