Peruvian President Alejandro Toledo has called on the two candidates in Sunday's run-off presidential vote to ensure it is fair and transparent.
Ex-army officer Humala is a political unknown
"It is the duty of everyone, above all the candidates, to make sure the elections are clean and orderly," Mr Toledo said in a televised address.
Ex-president Alan Garcia and former army officer Ollanta Humala hold their final election rallies on Thursday.
Opinion polls suggest Mr Garcia is ahead of Mr Humala.
President Toledo said security measures would be in place "before, during and after" the 4 June election.
He said Mr Garcia and Mr Humala and their supporters had a responsibility to maintain a serene and orderly attitude, or risk weakening Peru's democratic institutions.
Mr Toledo also said the elections should be free of foreign interference, which correspondents say is a clear allusion to the Venezuelan President Hugo Chavez, who has openly backed Mr Humala and criticised Mr Garcia.
Alan Garcia has been a political figure in Peru for many years
Sunday's election was "for Peruvians and between Peruvians", Mr Toledo said.
Mr Humala, a self-proclaimed nationalist, launched a series of campaigns on his rival during a Wednesday night rally in the capital, Lima.
Alan Garcia was going to be "a pawn of the United States", he told supporters.
For his part, Mr Garcia said Mr Humala, if elected, would follow President Chavez's anti-US rhetoric.
"I represent the democratic alternative without vestiges of totalitarianism, dictatorship," Mr Garcia told the Radioprogramas radio station.
The election campaign draws to a close on Thursday. Mr Humala will be in the city of Cuzco, while Mr Garcia is due to hold a rally in the centre of Lima.