Egypt’s opposition National Salvation Front has urged supporters to vote “No” in a looming referendum on a controversial draft constitution.
However, it said it could still call a boycott if its demands for the ballot – including the judiciary acting as overseer – were not met.
The opposition says the draft document, backed by President Mohammed Morsi and his supporters, is too Islamist.
The controversy has prompted mass demonstrations across Egypt.
In a separate development, conciliation talks called for Wednesday by the head of the armed forces have been postponed, with no new date announced.
The National Salvation Front on Wednesday spelled out its stance on the referendum, issuing a call to Egyptians to “go to polling stations to refuse the proposed constitution and to vote ‘no'”.
Leading opposition politician and former Arab League chief Amr Moussa told Reuters news agency: “We will vote ‘no’.”
An already confused situation in Egypt has quickly become even more confusing. The opposition has finally decided to urge supporters to take part in the referendum on the new constitution and to vote “No”.
But it has imposed several conditions that could prove impossible for the government to meet.
The opposition also agreed to take part in reconciliation talks hosted by the army. But then, for some unknown reason, the army delayed the talks from Wednesday and did not fix a new date.
Even the date of the referendum is not clear, with some government sources reporting that it will be held over two days, others that it will just be on Saturday.
But another leading opposition figure, Hamdeen Sabbahi, told a news conference the Front could still call for a boycott if key conditions were not met. They included:
Correspondents say it is far from certain these conditions can be met, as thousands of judges have already refused to take part.
Voting has already begun in embassies and consulates abroad, but there is still much confusion over the domestic vote, particularly whether it will be held over the next two weekends or on 15 December alone as demanded by the opposition.
Further confusion arose when the military said a national unity meeting aimed at calming the crisis had been delayed “because reactions to it were not at the level wished for”.
Only moments before the postponement, the opposition had made it known that it was prepared to take part.
Defence Minister Abdel Fattah al-Sisi thanked those who had responded to the invitation but said the talks were being postponed to an unspecified later date.
As tensions surrounding the vote grew, thousands of protesters took to the streets of Cairo on Tuesday in rallies both for and against the proposed constitution.
The streets of Cairo were described as calm on Wednesday and army tanks remained deployed outside the presidential palace.
Last weekend, the president offered a concession to the opposition by annulling a 22 November decree that gave him sweeping new powers.
However, some rulings of the controversial decree – which stripped the judiciary of any right to challenge his decisions – still stand, and a number of opposition figures dismissed the concession as a political manoeuvre.
