Peru's interim President Francisco Sagasti hit out on Friday against retired members of the armed forces who called for the military to prevent leftwing candidate Pedro Castillo from assuming the presidency.
Unionist Castillo is expected to be declared the winner of the June 6 second-round presidential run-off when final results are eventually published.
An unofficial count has him beating rightwing populist Keiko Fujimori — who claims the election was marred by fraud and has asked for it to be annulled — by around 44,000 votes.
On Thursday, hundreds of retired members of the armed forces signed a letter denouncing "fraud" and asking the military high command to prevent Castillo from being proclaimed president by the National Elections Jury (JNE) in an "illegal and illegitimate" manner.
"It's unacceptable... that a group of retired members of the armed forces try to incite the Army, Navy and Air Force high command to break the rule of law," said Sagasti.
"In a democracy the armed forces are not partial, they are absolutely neutral and scrupulously respectful of the constitution," added Sagasti, who is due to hand over the reins on July 28.
The letter was delivered to the combined high command headquarters in the capital Lima.
A similar letter signed by 64 retired generals and admirals — voicing their opposition to a Castillo election victory — was released on Monday.
The JNE is still dealing with challenges to the results brought mostly by Fujimori's campaign.
Sagasti said he had asked Defense Minister Nuria Esparch to send the letters to the public prosecutor's office to "conduct the necessary investigations to determine if there was conduct that was potentially harmful to constitutional order and to establish those responsible."
Fujimori first cried foul once Castillo moved ahead of her in the official vote count. Early on she had been in the lead.
The daughter of disgraced and authoritarian former president Alberto Fujimori counts much of her support base in the big cities, where counting is quicker, while Castillo's bastion is the countryside.
Observers from the Organization of American States have described the election as "clean" and without "serious irregularities."
Three days before the election, the armed forces urged Peruvians to "respect" the results.