Most of them kill because their husbands have taken a new wife or mistress, or after suffering years of domestic violence, according to the Egyptian National Centre for Social and Criminal Studies.

It says most of the murders are carried out by housewives aged 20 to 40. In some cases the women mutilate the bodies of their partners as a form of revenge.

The Egyptian interior ministry says the number of women convicted of murdering their husbands increased from 18 in 1997 to 21 last year.

A BBC correspondent in Cairo says these figures may not seem startling, but will come as a great shock to traditionally conservative Egyptian society.

'Honour crimes'

The Centre for Social and Criminal Studies reviewed the cases of 40 women convicted of murder.

It found that most of the killings took place during the hot summer months in the overcrowed capital, Cairo. Such incidents were rare in rural areas in southern Egypt.

Most of the women were sentenced to death or life imprisonment.