DAMASCUS — Islamic State insurgents have opened an office in northern Syria where single women and widows can register to marry fighters from the radical al Qaeda offshoot, a monitoring group said on Monday.

The office in al-Bab, a town northeast of Aleppo city, records the names and addresses of the women so that Islamic State militants can go to their families and make a formal offer of marriage, the Syrian Observatory for Human Rights said.

The Observatory, which cited sources in al-Bab and Aleppo, is based in Britain and relies on a network of people on the ground in Syria to report information. It was not immediately possible to confirm the report independently.

There have been previous reports of militants seeking wives or forcing women to marry them in areas where the group has been active. The Observatory’s director, Rami Abdurrahman, said it was the first time he had heard of the group setting up a formal office to register potential spouses.

Islamic State has set strict limits on women’s rights in areas it controls. A group statement issued last week said women in the Iraqi city of Mosul, which the rebels captured in June, had been warned to wear full-face veils or risk severe punishment. The statement also listed guidelines on how veils and clothes should be worn, part of Islamic State’s campaign to forcibly impose their radical brand of Islam.

More moderate rebels launched a major offensive against the Islamic State in January and have pushed them out of large swathes of Aleppo province, although the two sides still clash regularly.