The Kerala [Images] police have registered cases of sedition and criminal conspiracy in connection with an e-mail containing threats to President A P J Abdul Kalam and Prime Minister Manmohan Singh [Images], who is visiting Kerala next week.

The police are questioning four persons, including the owner of the cyber cafe from where the e-mail was sent to various senior officials of the state.

The e-mail also contained references to Parliament attack case convict Mohammed Afzal Guru and Abdul Nasser Madani, an accused in the 1998 Coimbatore blasts and who is now lodged in a jail in Tamil Nadu.

Apart from the owner of cyber cafe, which has been sealed by the police, others being questioned are two of his female employees and a watchman.

Twelve persons are said to have visited the cafe on October 26 when the mail was sent to at least 20 top officials of the state, including the director-general of police and the home secretary, police sources said.

Two cases under Sections 506 (sedition) and 120 (criminal conspiracy) of the Indian Penal Code were registered at the Central Police Station.