The interrogation came despite a request by Castillo's lawyers to annul the investigation, arguing sitting presidents have legal immunity during their five-year term under the South American country's constitution.

"I'm an honest man and I will always defend my innocence and honour," Castillo wrote on Twitter after the session, stressing he has not committed any corrupt acts.

Prosecutors previously said they opted to investigate Castillo "due to the seriousness and degree" of accusations that his former transport minister, Juan Silva, engaged in corrupt acts the president would know about.

Silva, who received offers from the prosecution to co-operate, is currently in hiding.

Upon leaving the prosecutor's office, Castillo briefly told reporters he answered all questions put to him.

"We are willing to continue responding, because Peru needs us to clarify things," he said.

The prosecution have not yet indicated whether Castillo will be recalled for further questioning.

The leftist president's government faces other corruption investigations along with social protests that have tanked his popularity after just 11 months in office.

At the end of March, Castillo overcame a second attempt by the opposition to impeach him. after they cited his "moral incapacity" to govern.

Australian Associated Press