Lourdes Flores, the conservative candidate, accused Ollanta Humala, the front-runner and retired army general, of threatening to interfere with Sunday's election result by hinting at a coup.
Alan Garcia, the populist candidate and former prime minister, went further and said Humala had "a dictatorial message such as threats of executions and calls to behead corrupt people".
Garcia was referring to comments from Humala's mother calling for homosexuals to face the firing squad and corrupt politicians to be executed.
The attacks on Humala came a day after he said he was certain that, should Flores be elected, she would be overthrown within a year.
'Disaster and failure'
Far from forming a pact against Humala, Garcia and Flores also had sharp words for each other.
Flores, who is seeking to be the country's first female president having failed twice previously, called Garcia "the candidate of disaster and failure", referring to his 1985-1990 presidency that was marked by inflation and endemic corruption.
Garcia played on the perception of Flores as the candidate of wealthy Peruvians, saying: "Peru should not choose between military dictatorship and the dictatorship of money."
Flores (R) has accused Humala
of hinting at a coup
Twenty candidates are standing in Sunday’s poll but Humala, Garcia and Flores have long been the only three serious contenders.
Opinion polls give Humala 32% of the vote, but predict that none of the candidates will secure a big enough majority to be elected outright, meaning a run-off between the top two in May.
Humala has courted controversy throughout the campaign with his direct manner and hardline policies but has apparently tapped into a powerful vein of discontent among Peru's impoverished majority.
He is an ideological adherent of Peru's 1968-75 left-wing military dictator General Juan Velasco and has pledged to punish a ruling class widely perceived as corrupt by promising heavy state intervention in the currently free-market economy.
Humala led an aborted coup in 2000 and has been endorsed by Hugo Chavez, the Venezuelan president. He is is seeking to emulate the recent victory of Evo Morales in Bolivia by gaining the votes of Peru's indigenous population.
Garcia meanwhile has sought to align his ideological vision with the more moderate left-leaning, US-friendly South American leaders such as Brazil's Inacio Lula da Silva of Brazil and Chile's Michelle Bachelet.
On Wednesday, he told thousands of supporters in Lima's port of Callao that he is the man in the middle: Peru's best hope to defeat raw capitalist greed and extreme nationalism.
Should Garcia finish in the top two, it will signify a remarkable comeback for a man whose five-year tenure as president until 1990 left a legacy of crippling hyperinflation, surging guerrilla violence and corruption and saw him spend nearly nine years in exile.
"Peru should not chose between military dictatorship and the dictatorship of money"
Analysts attribute Humala's popularity to growing disenchantment with traditional politics.
A recent UN report said 73.5% of Peruvians believe they need an authoritarian government and only 5.6% believe the South American country has had good governments.
The long shadow cast by Alberto Fujimori, the former president who left power in 2000, still lingers as his daughter Keiko looks set to win a congressional seat in the elections.
Her father, meanwhile, has been busy despite being jailed in Chile. He has married Satomi Kataoka of Japan, 28 years his junior.