Egypt is due to announce the official results of a referendum on a controversial draft constitution.
Early unofficial results suggested more than 60% of voters said "yes" to the document, which is endorsed by Islamist President Mohammed Morsi.
But the opposition, which says the draft favours Islamists, is demanding an inquiry into alleged voting fraud.
Opposition spokesman Amr Hamzawy said: "We are asking the commission to investigate the irregularities."
The BBC's Middle East editor Jeremy Bowen explained that Egypt has seen large and occasionally violent demonstrations by the opposing sides in the past few weeks.
Mohamed ElBaradei, Nobel peace laureate and founder of the Constitution Party, told Today programme presenter Evan Davis that Egypt is still "paying the price of 60 years of oppression".
"The county is deeply divided," he said, "and the constitution, if adopted, will simply institutionalise instability."
"The economy is falling apart [and] law and order is almost absent.... we are not in the greatest shape on the eve of Christmas Day," he added.
Get in touch with Today via
or text us on 84844.