Fighters of the self-declared Islamic State have killed some 146 people in a house-to-house massacre of civilians in the Syrian border town of Kobani, a conflict monitoring group says, calling it the second-worse such mass killing by the Islamist extremists since last year.

NPR's Deborah Amos, reporting from southern Turkey, says the Britain-based Syrian Observatory for Human Rights has spoken to witnesses who reported the shooting spree.

Citing medical sources in Kobani, the Syrian Observatory said the civilians "were executed by [the Islamic State] in their homes or killed by the group's rockets or snipers," Rami Abdel Rahman, the Observatory's director said. The group said that militants "fired at everything that moved."

The Associated Press quotes Kobani-based Kurdish activist Mustafa Bali as saying "that small groups of jihadis are still in the town and have taken civilians hostage in at least three locations." At a restaurant where hostages had been taken, Kurdish fighters stormed the building and freed the captives, Bali told the AP.

"The militants launched twin attacks on Thursday, in Kobani, also farther east in one of the last government held areas in northern Syria," Deborah says. "More than 60,000 people are now displaced, according to the United Nations [and] another 200,000 may yet flee as ISIS fights take over areas formerly held by the regime" of Bashar al-Assad.

The reported massacre comes a day after the Islamic State launched an attack to recapture the city after being forced out in January after fierce battles with Kurdish fighters.

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