Eight people were killed on Thursday in clashes between security forces and protesters in Ayacucho, according to local authorities, after a Supreme Court panel ordered an 18-month pretrial detention for Castillo while he is investigated over charges of "rebellion and conspiracy".
Demonstrators are calling for early elections, the closure of congress, a constituent assembly and the resignation of new President Dina Boluarte, who took over from Castillo after he was removed from office by a congressional vote hours after he attempted to dissolve congress.
Castillo has denied wrongdoing and says he remains the country's lawful president.
The death toll from the protests could be as high as 20, Eliana Revollar, head of Peru's ombudsman's office, said in an interview with local radio RPP.
In Ayacucho, protesters set fire to the local judiciary and prosecutor's offices, and security forces used weapons to repel attacks on the airport and other places, Revollar said.
A criminal complaint has been filed with prosecutors specialising in human rights in the Ayacucho province of Huamanga in order to determine "responsibility for the serious violations" there, the ombudsman's office said in a statement, without giving further details.
Boluarte's government announced a state of emergency on Wednesday, granting police special powers and limiting freedoms including the right to assembly, but it appears to have had little effect in stemming the protests.
