CAIRO – More than 22 million Egyptians have signed a petition calling for the country’s Islamist president to step down, the youth group leading the signature campaign said Saturday on the eve of mass protests aimed at forcing Mohammed Morsi from office.

The planned demonstrations, which could plunge Egypt once again into a dangerous round of civil unrest, reflect the growing polarization of the nation since Morsi took power, with the president and his Islamist allies in one camp and seculars, liberals, moderate Muslims and Christians on the other.

Already, clashes across a string of cities north of Cairo over the past week have left at least seven people dead, including an American teacher, Andrew Pochter of Chevy Chase, Md., who was stabbed by a protester while observing the demonstrations, his family said. Hundreds more have been injured, and there are deep-rooted fears in the country that Sunday’s protests will turn violent and quickly spiral out of control.

On Saturday, an Associated Press reporter saw Morsi supporters at a Cairo sit-in doing military-style fitness drills, with some wearing homemade body armor and construction helmets and carrying sticks. They said they had no intention of attacking opposition protesters, and would only act in self-defense or to protect the presidential palace.

The Tamarod, or Rebel, youth movement says its petition is evidence of the widespread dissatisfaction with Morsi’s administration, and has used the signature drive as the focal point of its call for millions of people to take to the streets Sunday to demand the president’s ouster.

Mahmoud Badr, a Tamarod leader, told reporters Saturday a total of 22,134,460 Egyptians have signed the petition. He did not say whether there had been an independent audit of the signatures.

Morsi’s supporters, who have long doubted the validity and authenticity of the collected signatures, expressed skepticism about the final count.

“How do we trust the petitions?” asked Brotherhood member Ahmed Seif Islam Hassan al-Banna. “Who guarantees that those who signed were not paid to sign?”

If authenticated, the collection of so many signatures would deal a symbolic blow to Morsi’s mandate and put in stark terms the popular frustrations with an administration that critics say has failed to effectively deal with the country’s pressing problems, including tenuous security, inflation, power cuts and high unemployment.

Tamarod announced its final tally the day before protests that organizers vow will bring millions into the streets to push the president from power.

Egypt has been roiled by political unrest in the two years since the uprising that ousted autocrat Hosni Mubarak, but the round of protests set to kick off Sunday promises to be the largest and holds the potential to be the bloodiest yet.