The jihadist group's office is operating from Al-Bab, a town in Aleppo province of northern Syria, for “single women and widows who would like to marry IS fighters”, said the Syrian Observatory for Human Rights.
The Britain-based monitoring group, citing residents, said interested parties were being asked to provide their names and addresses, “and IS fighters will come knocking at their door and officially ask for marriage”.
The IS has also expanded into tourism, taking jihadists on honeymoons and civilians to visit other parts of its “caliphate”.
Running twice-weekly tours from Syria's Raqa to Iraq's Anbar, IS buses fly the group's black flag and play jihadist songs throughout the journey.
IS proclaimed a “caliphate” last month straddling the two neighbouring Arab states.