CAIRO – Egypt´s election commission confirmed Thursday that the mother of a popular Islamist presidential hopeful was an American citizen, effectively disqualifying him from the race and likely boosting the chances of the Muslim Brotherhood´s candidate.

The ruling is likely to draw an uproar from supporters of Hazem Abu Ismail, a 50-year-old lawyer-turned-preacher who in recent months vaulted to become one of the strongest contenders for president, with widespread backing from ultra-conservative Muslims known as Salafis.

The announcement is particularly embarrassing for Abu Ismail, who used anti-U.S. rhetoric in his campaign speeches and rejected "dependency" on America. In recent weeks, he repeatedly denied reports that began circulating that his late mother held U.S. citizenship.

A law put in place after last year´s fall of President Hosni Mubarak stipulates that a candidate may not have any other citizenship than Egyptian — and that the candidate´s spouse and parents cannot have other citizenships as well.

The commission, however, did not outright disqualify Abu Ismail because it has not yet begun the process of vetting would-be candidates´ applications.

Abu Ismail is likely to fight for a way to stay in the race. Late Thursday, he urged his supporters to be patient because he was still fighting to prove that his mother´s documents didn´t amount to a full citizenship. He said the controversy was a mere plot to "slander" him.

"It has become clear to us that there is a big and elaborate plot, tightly prepared for a long time from many directions, internally and externally," he said, without naming anyone.

Before the commission´s announcement, Abu Ismail´s campaign was vowing to hold a huge rally in Cairo´s Tahrir Square on Friday against what they see as a conspiracy to keep him out of the race.

"The massive army of his supporters will rally because we will not be silent over forgery and games," said his campaign chief Gamal Saber.

As Sunday is the cut-off date for hopefuls to apply to run, the field for the May 23-24 election is beginning to become clearer after weeks of uncertainty. Barring last minute surprises, it appears to be headed to a contest focused between the Brotherhood candidate Khairat el-Shater and largely former regime figures, the popular ex-foreign minister and Arab League chief Amr Moussa and a former prime minister, Ahmed Shafiq.

Abu Ismail´s disqualification would remove el-Shater´s main competitor for the powerful Islamist vote. The Brotherhood, which is the country´s strongest political movement, announced last weekend that el-Shater — its deputy leader — would run. Since then, el-Shater has been heavily courting Salafis, a movement that is more hard-line than the fundamentalist Brotherhood.

Another significant Islamist candidate remains, Abdel-Moneim Abolfotoh, a reformer who was thrown out of the Brotherhood last year and is trying to appeal both to religious and more secular-minded Egyptians.

Moussa´s chances were boosted Wednesday when former Mubarak-era strongman and intelligence chief Omar Suleiman announced he would not run. Though widely distrusted as a symbol of the old regime, he might have found support among the liberals and moderates that Moussa is courting and who fear the Islamists´ rising power.

On Thursday, the 61-year-old el-Shater waved at some 3,000 supporters chanting, "Islam is back," as he entered the election commission headquarters to formally submit his papers to run. He handed in more than 250 endorsements from lawmakers from the Brotherhood party and the Salafi Al-Nour Party, needed to qualify to join the race.

To run for president, a candidate needs endorsements from lawmakers or a party. Otherwise, the candidate must gather some 30,000 endorsements from the public across different parts of Egypt.

Just a week ago, Abu Ismail flexed his muscles by submitting his documents amid a giant rally by his supporters, who stretched from his home to the commission headquarters. He handed in some 150,000 public endorsements, five times the required number.

His face — smiling, with a long, conservative beard — had become ubiquitous in Cairo and other cities because of a startlingly aggressive postering campaign that plastered walls and lampposts with his picture and the slogan, "We will live in dignity."

Abu Ismail rose to fame through his religious sermons and TV programs promising to guide Muslims to the "right path to Islam." He joined early on in the protests against Mubarak last year and after his fall struck a defiant tone against the military generals who took power.

When reports concerning his mother began circulating, Abu Ismail insisted she only had a Green Card to visit her daughter, who is married to an American, lives in the United States and has citizenship there.

But in a statement Thursday on the state news agency MENA, the election commission said it received documents from the Interior Ministry proving that Abu Ismail´s mother had a U.S. passport she used to travel a number of time to the U.S.. The mother also traveled to Germany and Egypt using the U.S. passport in 2008 and 2009, it said.

The commission starts reviewing would-be candidates´ papers after Sunday´s deadline. (© 2012 The Associated Press 04/05/12)