Egyptian President Mohamed Morsi was criticized for a power grab that supporters said helped advance the democratic processes in the country. A draft constitution, criticized for its enshrining of certain Islamic principles, heads for a national vote Saturday.
The National Salvation Front, a movement led by opposition leaders Mohamed ElBaradei and Amr Moussa, called for a "no" vote in the Saturday referendum.
"We hoped that the Egyptian president would cancel the referendum or at least postpone it but it seems that this is not an option now that voting has already started abroad, so we have decided to call on all Egyptians to vote against the constitution," the movement's spokesman, Hussein Abdel-Ghani, was quoted by Egyptian news agency al-Ahram as saying.
Recent frustration with Morsi, elected in June, follows growing concern about the role of the Muslim Brotherhood in post-revolution Egypt. Morsi was the candidate from the Muslim Brotherhood's Freedom and Justice Party.
Human Rights Watch, in a lengthy report published Wednesday, called on the public prosecutor's office to investigate what it said was the illegal detention of anti-government protesters by the Muslim Brotherhood last week.