Militants of the Islamic State group captured at least 50 civilians during a raid on a Syrian village and are holding them hostage, the Syrian Observatory for Human Rights said on Friday. 

The U.K.-based observatory reported ISIS had kidnapped the villagers from Mabujeh in the central province of Hama on March 31, according to Agence France-Presse (AFP). The news had been kept secret because of ongoing negotiations for their release, but the talks have fallen through, according to the group’s head, Rami Abdel Rahman.

Ten of those taken are believed to be Shiites. The remaining 40 subscribe to Sunni Islam, including at least 15 women. "There are fears that the women are being taken as slaves," Rahman told AFP, echoing previous concerns over the group’s treatment of female prisoners, which allegedly include sex slavery and human trafficking.

ISIS considers the Shiite Ismailis to be heretics, and the Sunnis, though they subscribe to the same sect as the militant group, were accused of being “loyal” to the Ismailis.

ISIS had previously executed 37 civilians, including children, in Mabujeh by "burning, beheading, and firing on them," according to the Observatory. Mabujeh has a population of Sunnis, Ismailis and Alawites -- members of the same sect as Syrian President Bashar Assad.

The latest abduction is part of ISIS’ strategy of targeting local minority groups, including Shiite Muslims, Yazidis, Kurds and Assyrian Christians. It has also gone after Sunni Muslims whom it has accused of sheltering or aiding members of the other sects.