Islamic State militants have reportedly kidnapped scores of Christians in northeastern Syria. The Britain-based Syrian Observatory for Human Rights said 90 Assyrian Christians have been captured, while another group put the number between 70 and 100. The captures came as ISIS militants retreated from Kurdish militia backed by the U.S.-led coalition. The Obama administration, meanwhile, is planning a major offensive in Iraq to retake the ISIS-controlled city of Mosul. Speaking in Kuwait Monday after meetings with top U.S. officials, new Defense Secretary Ashton Carter vowed to defeat the Islamic State.

Ashton Carter: “Our discussion this afternoon affirmed the seriousness and the complexity of the threat posed by ISIL (Islamic State), especially in an interconnected and networked world. Lasting defeat of this brutal group can and will be accomplished.”

Earlier this month, ISIS released video of the beheading of 21 Egyptian Coptic Christians in Libya. Amnesty International has now accused Egyptian forces of failing to take key precautions before launching retaliatory airstrikes, which killed seven civilians in the Libyan city of Derna.