Protesters said the center-right politician should be thrown from the race because pictures and video show her and a running mate handing out gifts and prizes at rallies in possible violation of a new law against vote-buying.
Electoral authorities are investigating the accusations.
Fujimori, the 40-year-old daughter of imprisoned ex-president Alberto Fujimori, has dismissed the accusations as “absurd.” Her press officer did not immediately respond to requests for comment outside regular working hours.
One of Fujimori’s rivals was thrown out of the race on Wednesday for giving cash to poor voters while campaigning. Her biggest obstacle to winning, Julio Guzman, was disqualified because his party did not comply with electoral procedures – a decision he called “fraud” that threatens to tarnish the legacy of the next president.
The electoral board has denied wrongdoing or political bias.
The U.S. Department of State said it was closely following Peru’s electoral process and that the ambassador to Peru had spoken with Guzman, a spokesperson told Reuters Friday.
Protesters chanted “Stop Keiko!” at the headquarters of the National Jury of Elections, which issued a statement urging the news media to “contribute to a climate of peace.”
“People are rising up to say enough of these irregularities and the Fujimori ambition of returning to power,” said Jorge Rodriguez, an organizer of a group called Fujimori Never Again.
Fujimori, who narrowly lost her first presidential bid in 2011, has long been the favorite for this year’s race.
She inherited a solid stock of support from her father, whom many credit with ending a bloody insurgency and fixing the economy in the 1990s. But many Peruvians despise her for her links to his authoritarian government, even after she has softened her once staunch defense of him.
Alberto Fujimori, who made Keiko Fujimori his first lady at 19 when he divorced her mother, is carrying out a 25-year sentence for human rights abuses and corruption.
A Reuters witness put the number of protesters, most of them young, at between 2,000 and 3,000. The rally largely peaceful and followed similar demonstrations against Fujimori in the Andean city of Cusco that upended her campaign event Thursday.
Elections are scheduled for April 10. A run-off would be held June 5.