Peruvians are casting ballots Sunday in a presidential run-off pitting the daughter of imprisoned former President Alberto Fujimori against leftist former army officer Ollanta Humala.

Participating in elections is mandatory for Peru's nearly 20 million eligible voters.

In the first round of balloting in April, Humala won 32 percent of the vote, falling short of the 50 percent margin needed for an outright win. Keiko Fujimori, a conservative candidate, took 24 percent.

Some voters are concerned that as president, Keiko Fujimori would try to free her father, who is serving a 25-year prison sentence for his role in death squad killings in the 1990s. Keiko Fujimori has apologized for mistakes and crimes committed while her father was president from 1990 to 2000.

Humala led an uprising against Alberto Fujimori in 2000, but lost a run-off election to current President Alan Garcia in 2006. Humala was outspoken during that campaign about his admiration for Venezuelan President Hugo Chavez, but he has since distanced himself from the leftist leader.

Much of the current presidential campaign has focused on continuing Peru's rapid economic growth of recent years, while ensuring that the poor also see some of that increased prosperity.