A Rio de Janeiro policeman has confessed to murdering Greece’s ambassador to Brazil at the direction of the diplomat’s wife, with whom he was having an extramarital affair, police say.

Ambassador Kyrakos Amiridis, 59, went missing Monday night and his Brazilian wife Francoise Amiridis, who he has a 10-year-old daughter with, reported him missing to police on Wednesday.

Officer Sergio Gomes Moreira Filho, 29, told police he killed the ambassador late Monday night in the Rio de Janeiro home the ambassador shared with his wife, which was located near her family’s residence in Nova Iguacu.

Ms Amiridis, 40, and Mr Filho had arranged the murder a few days in advance, investigator Evaristo Magalhaes said.

Greek diplomat Kyrakos Amiridis went missing on Monday night.

Both Mr Amiridis’s wife and the officer are in custody. Mrs Amiridis has admitted to the affair but has denied any role in the alleged plot.

Police have also detained a cousin of the officer, who Mr Magalhaes said acted as a lookout while the crime was committed and helped carry the body from the house with the promise he would be paid 80,000 reais ($34,100).

Mr Magalhaes said blood was found on a couch inside the ambassador’s home and he was likely stabbed to death, as no shots were reported in the area.

But he said it was not yet possible to determine the exact cause of death, because the policeman had burned the ambassador’s body in an attempt to cover up the crime.

A burned corpse was found on Thursday evening inside the boot of a car Mr Amiridis and his wife had rented.

It was parked under a highway overpass in the area where the couple had been staying.

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According to Mr Magalhaes, Francoise said she couldn’t stop Filho (pictured above) from killing her husband and insisted she was not at home at the time of the crime.

But the police investigator said in a press conference late Friday that the “evidence clearly puts the ambassador’s wife as a co-author of the crime.”

He said she started plotting with her lover to kill the ambassador after the couple had a serious fight three days before Christmas.

A burned corpse was found in an abandoned rental car on Thursday evening.

“All our evidence suggests that her motivation was to use the financial resources left by the ambassador so she could enjoy life with Sergio,” Mr Magalhaes said.

“This was a tragic, cowardly act, but we worked tirelessly to crack this case as soon as possible.”

Brazilian President Michel Temer, in a letter addressed to Greek Prime Minister Alexis Tsipras, said the ambassador’s killing had caused him profound sadness and he extended his condolences to the ambassador’s family, friends and the Greek people.

The Greek embassy in Brasilia declined to comment.

In Athens, Greek foreign ministry spokesman Stratos Efthymiou said the Government also had no comment.

Mr Amiridis served as Greece’s consul general in Rio from 2001 to 2004. He was Greece’s ambassador to Libya from 2012 until he took the top Brazil post at the beginning of 2016.

– with AAP