In the assault, the militants took between 70 and 100 Assyrians captive, said Nuri Kino, the head of the activist group A Demand For Action, which focuses on religious minorities in the Middle East. He said some 3,000 people managed to flee the onslaught and have sought refuge in the cities of Hassakeh and Qamishli.

The extremist fighters swept through the villages nestled along the banks of Khabur River near the town of Tal Tamr in Hassakeh province around dawn on Monday. The area is predominantly inhabited by Assyrians, an indigenous Christian people who trace their roots back to the ancient Mesopotamians.

The Britain-based Syrian Observatory for Human Rights said Thursday that the militants have picked up dozens more Christian Assyrians from 11 communities near the town of Tal Tamr in Hassakeh province in the past three days.

Syrian activists say the number of Christians abducted by Islamic State militants in northeastern Syria has risen to 220. IS began abducting the Assyrians on Monday, when militants attacked a cluster of villages along the Khabur River, sending thousands of people fleeing to safer areas.

Kino said his organization based its information on conversations with villagers who fled the onslaught and their relatives.The Britain-based Syrian Observatory for Human Rights also reported the abductions, but put the number of Assyrians held by the Islamic State group at 90. The Observatory relies on a network of activists inside Syria.Both activist groups said that most of the captives come from the village of Tal Shamiram, located some 85 kilometers (50 miles) southwest of the provincial capital of Qamishli.

An Assyrian woman from Tal Shamiram who now lives in Beirut said she has been scrambling to find out what has become of her parents as well as her brother and his wife and kids.

“Land lines have been cut, their mobiles are closed,” she told The Associated Press. “Have they been slaughtered? Are they still alive? We’re searching for any news.”

She spoke on condition of anonymity for fear of endangering relatives believed to be held by the militants.

“My family visited me last month and returned to Syria. There were clashes but it was normal, nothing exceptional. I feel so helpless, I cannot do anything for them but pray,” she said by telephone, her voice breaking.

The Islamic State group’s online radio station, al-Bayan, said in a report Tuesday that IS fighters had detained “tens of crusaders” and seized 10 villages around Tal Tamr after clashes with Kurdish militiamen. IS frequently refers to Christians as “crusaders.”

It was not immediately clear what the Islamic State group planned to do with the Assyrians.

The militants have a long history of killing captives, including foreign journalists, Syrian soldiers and Kurdish militiamen. Most recently, militants in Libya affiliated with the Islamic State group released a video showing the beheading of 21 Egyptian Christians.

But the Islamic State group also could use its Assyrian captives to try to arrange a prisoner swap with the Kurdish and Christian militias it is battling in northeastern Syria. There is a precedent: the extremists have released Kurdish school children as well as Turkish truck drivers and diplomats after holding them for months.