Egypt's opposition is calling for mass protests on Tuesday over alleged polling violations after Islamists backing President Mohamed Morsi claimed victory in the first round of a referendum on a new charter.
A group of top judges, meanwhile, announced on Monday it would boycott supervision of the second round, and Germany said it has postponed debt relief for Egypt because of concerns over the country's commitment to democracy.
Adding to the complications for Morsi, the prosecutor general named by the president as he temporarily assumed sweeping powers last month handed in his resignation, a judicial source told AFP.
"The prosecutor general has submitted his resignation under pressure from protesters," said the source, referring to magistrates who have been clamouring for his immediate departure.
The Supreme Judicial Council will examine prosecutor general Talaat Ibrahim Abdallah's resignation next Sunday, a day after the second and final round of voting in the referendum, the source said.
The opposition coalition, the National Salvation Front, urged Egyptians to "take to the streets on Tuesday to defend their freedoms, prevent fraud and reject the draft constitution" ahead of the second round.
It claimed "irregularities and violations" marred the initial stage of the referendum last weekend across half of Egypt that Morsi's Muslim Brotherhood said resulted in a 57 percent "yes" vote, according to its unofficial tally.
On the legal front, the State Council Judges Club, whose members took part in overseeing the first round as required by law, said it would boycott next Saturday's vote because the authorities had failed to live up to their promises.
The association has demanded that a "siege" of the Supreme Constitutional Court by Brotherhood supporters be lifted. But the action has continued without any intervention by the authorities, it said.
In Germany, a spokesman for the overseas development ministry said a plan to forgive up to 240 million euros ($316 million) of Cairo's debt had been delayed indefinitely.
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Germany's Development Minister Dirk Niebel said earlier he had serious reservations. "There is the danger that the dictatorial system of ousted president (Hosni) Mubarak is returning," he told the daily Berliner Zeitung.
Niebel said Berlin had cancelled talks on development aid scheduled for mid-December and that future assistance was dependent on Egypt's progress toward democracy and the rule of law.
Also increasing the pressure, Mohamed ElBaradei, the Salvation Front's coordinator and a Nobel Peace Prize laureate, renewed his call for Morsi to cancel the referendum altogether and enter talks with the opposition.
"Last chance: cancel the ill-reputed referendum and begin a dialogue to close the rift," he wrote on Twitter, although a spokesman for ElBaradei's group said the comment was not a call to boycott the second round.
Large protests both for and against the proposed constitution have been staged during the past three weeks, sparking violent clashes and revealing deep divisions in society over Morsi's rule.
Early this month, eight people were killed and more than 600 hurt when rival protesters fought outside the presidential palace in Cairo.
The opposition says the constitution weakens human rights, especially those of women, and undermines the independence of judges while strengthening the military.
It fears Islamists propelled into power after a revolution last year that toppled Mubarak's 30-year regime want to establish sharia-style laws.
Morsi, though, argues the slender majority he won in June presidential elections gives him a mandate for change and that the draft constitution is a key step to securing stability.
The opposition claims Saturday's first round of the referendum, which took place in the biggest cities of Cairo and Alexandria and in eight other regions, had numerous violations.
Those included monitors not being allowed into some polling stations, judges not present in all as required and some fake judges employed, and women prevented in some cases from casting their ballot.