The Muslim Brotherhood has warned that Egypt's fragile democratic gains are under threat, after a surprise court ruling overturned last year's parliamentary elections.

Egypt could see "dangerous" days ahead if power is returned to those linked to the previous regime, it said.

The group's candidate, Mohammed Mursi, faces ex-PM Ahmed Shafiq in a runoff presidential election this weekend.

The decision by the Supreme Court on Thursday plunged Egypt into turmoil.