Three Italian nuns were found killed in their Burundi convent on Sunday, officials have said.
The Italian foreign ministry confirmed the women were found dead at the Kamenge institution in a northern suburb of Bujumbura, the capital of the east-African nation.
Father Mario Pulicini, who is responsible for the parish, named the two nuns who were found in their dormitory as Lucia Pulici - who was 75 and due to celebrate her birthday on Monday - and Olga Raschietti, 82.
He said they were found decapitated in their dormitory on Sunday.
He told Reuters a third nun, 79-year-old Bernadetta Boggian, was found dead early on Monday morning. The killings appeared to have happened at separate times.
"It is very difficult to know the reason behind the killing, but nothing can justify it," Father Mario said.
Evidence showed that two of the nuns had been raped before they were killed, police spokesman Hermenegilde Harimenshi said. Mr Harimenshi was quoted by Reuters as saying they had been "partially decapitated.”
The Catholic diocese in Parma, Italy, said on its website that the death of Ms Pulici and Ms Raschietti appeared to have been "the tragic outcome of an armed robbery by a mentally unbalanced person".
Pope Francis has since responded to the tragic deaths by sending his condolences in a telegram to Bujumbura's archbishop.
The Holy See said he “learned with great sadness of the murder” of the three “faithful and devout nuns in these tragic circumstances”.
Police said three suspects had been detained for questioning.
Ms Pulici and Ms Raschietti had served in Burundi for seven years, after working several years in the east of another central African state, the Democratic Republic of Congo.
Independent News Service