A two-year-old boy has died from blood loss following a failed circumcision at a migrant centre in Italy.
The boy's twin brother also underwent the procedure in Rome's north-western suburb of Monterondo and is recovering in hospital.
A 66-year-old man has been charged with murder, according to Italian media.
Some 5,000 circumcisions are performed in Italy each year but more than a third are carried out illegally, according to health charity Amsi.
Cultural non-profit group Arci said the procedures had taken place at a refugee centre it runs with the local council in Monterondo.
"It is a tragedy that leaves us speechless," Arci said in a statement on Facebook, adding that it would take civil action once those responsible for the child's death had been determined by police.
The two boys, who have not been named, were born in Italy in 2017 to a Nigerian mother who has five other children in Nigeria.
Local media say the mother had asked for the operations in respect for Nigeria's Islamic traditions, despite being Catholic herself.
The medical credentials of the doctor are reportedly being questioned by police.
Ansa said the man arrested was an American citizen of Libyan origin.
"It is an absurd tragedy," said Antonino Lupi, mayor of Monterondo, in an interview with the Corriere Della Sera.
Circumcision is currently unavailable in public health institutions in Italy.
Having the procedure at a private clinic can cost between €2,000 (£1,798) and €4,000 (£3,596), according to Foad Aodi, president of Amsi.
As a result, those from poorer backgrounds can "end up in the hands of unscrupulous and unskilled people, who for €50 or €20 practise circumcision," Mr Aodi said in a statement.
By Michelle Roberts, BBC News Online health editor
Although it is a relatively simple medical procedure, circumcision is not entirely risk free.
Doctors may recommend that a man or boy is circumcised if he has an unusually tight foreskin, known as phimosis, or suffers from recurrent infections of the foreskin and penis, known as balanitis.
There is also some evidence that men who are circumcised have a lower risk of contracting HIV from HIV-positive female partners.
It is not clear if circumcision reduces the risk of other sexually transmitted infections too, but studies suggest it may lower the chance of catching genital warts caused by a family of viruses called HPV.
The main risks of the surgery are bleeding and infection.
In the UK, the chance of these occurring is between one in 10 and one in 50, according to the NHS website, although that is a figure for older boys and men, not newborns.
Circumcision is legal throughout Europe, although the practice is becoming more controversial.
A court in Germany passed a local ban in 2012 after the circumcision of a four-year-old Muslim boy led to complications, with the judge saying it "permanently and irreparably changed" the body.
However, the German government later that year clarified that the procedure is legal provided it is performed by trained practitioners.
The following year, the Council of Europe recommended countries take steps to ensure good medical and sanitary practices when performing a circumcision.
And in the UK in 2016, a court ruled that a Muslim father could not have his sons circumcised after their mother disagreed.