(Veiled women walk past a billboard that carries a verse from Koran urging women to wear a hijab in the northern province of Raqqa March 31, 2014. The Islamic State in Iraq and the Levant (ISIL) has imposed sweeping restrictions on personal freedoms in the northern province of Raqqa. Among the restrictions, Women must wear the niqab, or full face veil, in public or face unspecified punishments "in accordance with sharia", or Islamic law. REUTERS/Stringer )

(Veiled women walk past a billboard that carries a verse from Koran urging women to wear a hijab in the northern province of Raqqa March 31, 2014. REUTERS/Stringer )

Islamic State, the al-Qaeda offshoot that seized large swathes of northern Iraq last month, has warned women in the city of Mosul to wear full-face veils or risk severe punishment.

The Sunni insurgents, who have declared a caliphate in parts of Iraq and Syria and have threatened to march on Baghdad, also listed guidelines on how veils and clothes should be worn, part of a campaign to violently impose their radical brand of Islam.

“The conditions imposed on her clothes and grooming was only to end the pretext of debauchery resulting from grooming and overdressing,” said the Islamic State in a statement.

“This is not a restriction on her freedom but to prevent her from falling into humiliation and vulgarity or to be a theater for the eyes of those who are looking.”