The April 6 Movement (Democratic Front) has said that four of its members were arrested on Saturday in downtown Cairo for unknown reasons, as a security crackdown on activists critical of the authorities seems set to continue.

Spokesman for the front Mostafa Hegazy said during an interview with Al-Ahram's Arabic website that the whereabouts of the detained members remains unknown.

The front, a breakaway group from the April 6 Youth Movement, planned to stage a protest on Saturday but canceled it in order to avoid possible clashes with security forces amid the current inclement weather, according to Hegazy.

The canceled protest, Hegazy said, cannot therefore be the reason behind the arrest of the four members, named as Hamdy Keshta, Ahmed Fahmy, Ahmed Abou-Treika, and Maher Mohamed.

Protests that have not obtained the prior permission of state authorities are illegal, according to a law issued last month.

According to Hegazy, the detainees were near Mostafa Mahmoud Square in the up-market district of Mohandiseen in Giza, where the protest had been supposed to take place, when they were arrested.

Hegazy said one of the detainees managed to call him to inform him of the arrest.

Thousands of Islamist protesters have been detained since the summer, when the Muslim Brotherhood's Mohamed Morsi was ousted from the presidency. Since the issuing of the new protest law, security forces have also started arresting non-Islamist protesters and activists.

Among the detained are Ahmed Maher, co-founder of the April 6 Youth Movement, and Alaa Abdel-Fattah, a well-known blogger and rights activist. They are accused of inciting an unauthorised protest against military trials of civilians in Cairo last month.