CAIRO — Egypt’s top prosecutor ordered government ministries on Wednesday to enforce a ban on pornographic websites, three years after a court denounced the sites as ‘‘venomous and vile.’’

An official in the prosecutor’s office said the order followed a protest Wednesday by ultraconservative Muslims known as Salafis, who have launched a campaign called ‘‘Pure Net’’ to prohibit the pornographic websites. The official spoke on condition of anonymity because he was not authorized to speak to reporters.