Peru's presidential candidate Keiko Fujimori waves during her closing campaign rally in Lima, June 2, 2011. Peru's tight June 5 presidential election pits right-wing lawmaker Fujimori against left-wing populist Ollanta Humala.[Photo/Agencies]

LIMA -- Regional and European observers were calling for caution ahead of Sunday's Peruvian presidential runoff between Ollanta Humala and Keiko Fujimori, who were running a neck-to-neck race.

According to latest opinion polls, Fujimori, daughter of imprisoned former president Alberto Fujimori, and Humala, the candidate for the Peru Wins alliance, are virtually on a tie, as they vie to replace incumbent president Alan Garcia for a five-year term starting later this year.

EU representative Jose Salafranca hailed the Peruvian electoral system as "independent, transparent," but cautioned that "everybody must participate in the elections with responsibility" for the runoff.

"The world attention is on Sunday's elections of Peru," he said.

Former Argentine foreign minister Dante Caputto, head of the observers from the Organization of American States (OAS), said that in the first round of elections on April 10, "the candidates and electors acted with seriousness and responsibility, without producing incidents."

About 20 million Peruvians are expected to vote on Sunday.