A "mega-operation" netted the six who are suspected of involvement of "irregular promotions" in the police force, said a ministry statement.

Three of the six are active police generals suspected of having approved promotions, with Castillo's alleged blessing, in exchange for money.

The operation involved searches in several cities, including two homes in Lima of former defense minister Walter Ayala, also under investigation, said the ministry.

Both Ayala and Castillo have denied the charges.

A former commander of the army, General Jose Vizcarra, and of the air force, Jorge Chaparro, alleged in November that Castillo's government had put pressure on them to promote officers who did not qualify.

Castillo was removed from office and arrested on December 7 after trying to dissolve parliament to rule by decree in a failed attempt at a so-called self-coup.

Castillo, who was president for less than a year-and-a-half, now stands accused of rebellion and conspiracy and has been ordered held in pre-trial detention for 18 months.

The ouster of the former rural school teacher and union leader caused protests countrywide, with Peru's rights ombudsman reporting 22 people killed in clashes and more than 600 injured.