Police said Medhanie Yehdego Mered, thought to be the leader of a migrant smuggling ring, was extradited to Italy from Sudan late on Monday.
But relatives of the man brought to Italy, who was pictured in photos released by Italy's state police arriving in handcuffs in Rome, have told the British press that he is Medhanie Tesfamariam Kidane, a 27-year-old Eritrean refugee, and not Mered.
“The prosecuting team is carrying out investigations into the reports,” a spokesperson for Italy's police told The Local.
"There is nothing more to add at this stage."
Reports that Italian and British authorities, which assisted Italy in the investigation, got the wrong man emerged in the British press last night, just hours after news of the extradition of one of Europe's most-wanted men was delivered with much fanfare.
A woman in Norway who claimed to be the sister of the man arrested told the BBC's Newsnight that her brother was “completely innocent”.
Friends and relatives also said images of Kidane did not resemble the one of Mered which had previously been distributed by the UK's National Crime Agency (NCA).
"The identification of the suspect, his arrest, his handing over and his extradition to Italy were communicated to us in an official manner by the NCA and the Sudanese authorities through Interpol," chief prosecutor Francesco Lo Voi was quoted by the Italian media as saying on Thursday.
An NCA spokeswoman said "we're aware of the media reports. It's a bit too soon to speculate at the moment".
AFP also interviewed people in Sudan who said the detainee was not Medhanie Yehdego Mered.
Friends of the arrested man said his name was Mered Tesfamariam, and he was a 27-year-old migrant.
"I know this man since he arrived in Sudan in 2014, his name is Mered Tesfamariam. The person who has been taken to Rome is not the general. The man taken to Rome doesn't even speak Arabic," Eritrean Tasfie Haggose, 38, said in Khartoum.
"The general is well known among Eritreans, especially among those who have tried to cross the Mediterranean. The general moves secretly. He does not deal directly with people who want to migrate. He deals through mediators or brokers," he said.
Fellow Eritrean Barhi Kobron, 28, said he too knew the detainee.
"This man used to move freely among people, which is not how the general behaves. The general has no house in Khartoum. He moves between Sudan, Ethiopia, Libya, and between Khartoum and eastern Sudan."
Medhanie Yehdego Mered, on a wanted list since 2015 for people smuggling, is accused of packing migrants onto a boat that sank in 2013 off the island of Lampedusa, claiming at least 360 lives in one of the worst disasters in the Mediterranean.
Referred to in wiretapped conversations between his subordinate alleged traffickers as "the general", Mered is accused of organising the smuggling of up to 8,000 people a year on migrant boats.
Italy, Sudan and Britain had hailed his capture as a significant blow to the people smuggling business as Europe moves to stem the flow of migrants across the Mediterranean.
According to the UN's refugee agency (UNHCR), over 48,500 people have arrived in Italy by boat so far this year.
More than 10,000 people have died crossing the Mediterranean to Europe since 2014.