BEIRUT (AP) -- Islamic State militants have abducted at least 70 Christians, including women and children, after overrunning a string of villages in northeastern Syria, two activist groups said Tuesday.

The Sunni extremists, who follow a radical interpretation of Islam, have repeatedly targeted religious and ethnic minorities in Syria and Iraq since seizing control of large swaths of both countries. The group's fighters have ransacked churches, demolished Shiite and Sunni Muslim shrines, and enslaved women of the Yazidi community, a tiny sect they consider heretics.

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

During the raids, 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.

Kino said his organization based its information on conversations with villagers who fled the attack and their relatives.

The Britain-based Syrian Observatory for Human Rights also reported the abductions, but put the number of Christians 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 southwest of the provincial capital of Qamishli.

An Assyrian Christian 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.

The fighting around Tal Tamr has coincided with heavy clashes between Kurdish militiamen and Islamic State militants about 90 kilometers to the east near the Iraqi border. Kurdish fighters from the People's Protection Units, or YPG, launched an offensive over the weekend, quickly seizing some 20 villages from the extremists.

The fighting continued through Tuesday, as the YPG has captured another 10 villages, the Observatory said.