CAIRO (AFP) - An Islamist alliance opposed to the Egyptian military's ouster of president Mohamed Mursi called off rallies that they planned to stage in Cairo on Sunday, citing concerns about security.

"Several marches in Cairo have been cancelled for security reasons," said Yasmine Adel, a spokeswoman with the Anti-Coup Coalition.

She said some other marches were taking place, however, but it was not immediately possible to confirm.

In central Cairo's Dokki neighbourhood, residents took over a mosque the Islamists had planned to use as a starting point for a march and put up a poster of a slain policeman, an Agence France-Presse correspondent said.

Vigilantes stopped cars with bearded people and took them out, the correspondent said.