A toddler bled to death following a home circumcision at a refugee centre in Rome at the weekend.
Police opened a murder investigation into the incident and arrested a Libyan-born US citizen aged 66 in connection for manslaughter, the state prosecutor of Tivoli, Francesco Menditto said.
Italian media are describing the man as a self-proclaimed doctor.
The toddler was reportedly born in Italy in January 2017 to a Nigerian woman believed to have claimed asylum in Italy.
His twin brother also underwent the operation and was admitted to Sant'Andrea hospital but was later transferred to the pediatric intensive care unit at Gemelli Hospital in Rome.
"One of the two children, transported to the hospital S. Andrea in Rome, died of complications yet to be verified, while the other is currently hospitalised," Meditto said in a statement.
"A US citizen of 66-year-old Libyan descent was held responsible for practising a circumcision operation on two, two-year-old Nigerian brothers."
Hospital staff at Gemelli confirmed in a statement that the brother is in a stable condition.
The operation reportedly took place in a migrant centre apartment run by the charity Arci and the Monterotondo local council.
The centre is made up of nine apartments which host women and children asylum seekers.
"We are shocked to learn of the death of a child and the serious condition of his twin in Monterondo,” Arci said in a post to Facebook on Sunday.
“The two children are hosted in a welcome centre that Arci has run with Monterotondo Council since 2009. It is a tragedy that leaves us speechless. We are anxiously awaiting a medical update on the second child.”
Reports say the mother had arranged the operation in respect of her country's Islamic traditions.
Foad Aodi, founder of Amsi — an association of foreign doctors in Italy — said the incident is a "tragedy".
"We have been committed for years to the legality and the right of health and religious respect for all against all forms of do-it-yourself illegality and care, and clandestine circumcisions from unauthorized and clandestine personnel and facilities".
Aodi said more than 35% of circumcisions carried out in Italy are done so at home in a clandestine manner and blamed this on economic reasons and lack of authorised facilities.
He appealed for Italy's Ministry of Health to authorise circumcision at public and private health facilities at prices that are affordable to lower-income Muslim and Jewish families.
The cost of the operation at a private clinic can cost up to €4,000, Aodi said in a statement.
He added that those from lower income families can "end up in the hands of unscrupulous and unskilled people, who for €50 or €20 practise circumcision".
Euronews contacted Italy's ministry of health for comment and a representative from Arci.