An exiled Islamist group based in London says the Saudi authorities are holding in detention the sister of the exiled opposition figure Mohammad al-Masaari.

It said the woman, Suha Bint Abdallah al-Masaari, was detained a week ago when she returned to Saudi Arabia following a visit to London.

The Islamist group, Islamic Observatory, said she had committed no offence and it had appealed to the Crown Prince, Abdallah ibn Abdel Aziz, to secure her release.

Mohammad al-Masaari, who heads the Committee for the Defence of Legitimate Rights, has lived in Britain since 1994; three years ago, the British government unsucessfully sought in the courts permission to deport him to a third country.