A spat between presidential contender Keiko Fujimori and her younger brother over the future leadership of the political movement they inherited from their ex-president father could cost her key votes in Peru's tight June 5 run-off election.

Keiko Fujimori threatened to throw Kenji Fujimori out of her political party after he stoked fears that the family harbors dynastic intentions by saying he will run for president in the next elections in 2021 if she loses this year.

Keiko Fujimori had vowed that no one with the Fujimori surname would seek the presidency in 2021 before her brother declared on Twitter: "the decision is mine."