Egypt on Monday was awaiting official results of a referendum on a new constitution reportedly backed by two-thirds of voters but which the opposition alleged was riddled with fraud, AFP reports.
"No official date has been fixed" for the final polling figures, a member of the electoral commission, Mohamed el-Tanobly, told AFP. State media had reported the count could be given on Monday.
The Muslim Brotherhood backing President Mohamed Morsi and media say an unofficial tally shows 64 percent of ballots backed the new charter.
But the National Salvation Front opposition coalition claims numerous instances of polling "fraud and violations" and is demanding the electoral commission investigate before issuing its official figures.
"The referendum is not the end of the road. It is only one battle," the Front also said in a statement. "We will continue the fight for the Egyptian people."
The challenge suggested no quick end to Egypt's political crisis, which erupted a month ago when Morsi allocated himself near-absolute powers to push through the charter written up by an Islamist-dominated panel.
Fierce protests, including violent clashes on December 5 that killed eight people and wounded hundreds, led to Morsi giving up those powers early this month.
Egypt remains a deeply polarised nation.
Morsi and his Muslim Brotherhood, testing newfound power after decades of being sidelined by ousted leader Hosni Mubarak, are spearheading changes to infuse the country with a more Islamist character favoured by the vast poorer part of the population. They say the new constitution will usher in stability.
Against them are ranged the largely urban, liberal, leftwing, Christian and secular supporters of the opposition who feel alienated by Morsi. They see ambiguities inserted in the charter as opening the way to future sharia-style strict Islamic law.
Germany echoed the call for an investigation into the alleged voting fraud, saying the new constitution can only be seen as valid "if the process of its adoption is beyond reproach."
The United States, which provides Egypt's powerful military with $1.3 billion in aid per year, has kept mostly quiet on the turmoil buffeting its key Middle East ally.
But the Republican chairwoman of the Foreign Affairs Committee in the US House of Representatives, Ileana Ros-Lehtinen, called the vote "a defeat for the Egyptian people" at the hands of "an Islamic dictatorship."
Iran, which is trying to claim the ongoing Arab Spring was inspired by its own 1979 Islamic revolution, welcomed the referendum by saying it promoted "progressive, Islamic and revolutionary goals" in Egypt.
The political storm in Egypt has deepened economic instability triggered by Mubarak's overthrow in 2011.
Morsi's government is grappling with climbing debt, plunging tourism revenue, a tottering currency and fleeing investors.
A $4.8 billion loan from the International Monetary Fund was put on hold this month, adding pressure on Egypt's central bank, whose foreign reserves have more than halved since Mubarak's ouster to less than $15 billion.
State television announced on the weekend that the central bank chief, Faruq El-Okda, was resigning -- before rapidly citing a cabinet source denying that.
"I'm more worried about the economic future of the country today than I was just a few weeks ago," Angus Blair, a veteran financial analyst and head of the Signet Institute think-tank in Cairo, told AFP.
"Voting yes in the constitutional referendum will not stop the economic malaise," he said.