An Eritrean man detained by Sudanese police last month and then extradited to Italy accused of being a people smuggling kingpin has declared he is the victim of mistaken identity, in a potential embarrassment for Italian and British law enforcement.

Italian and British police claimed on Wednesday to have brought to Rome a notorious 35-year-old people-smuggler called Medhanie Mered, who once boasted of smuggling at least 13,000 people to Europe. But on the first day of pre-trial proceedings in Rome on Friday the suspect in custody said he was in fact Medhanie Berhe, a 29-year-old refugee unconnected to people smuggling, and stressed his innocence.

According to his lawyer, Berhe admitted that he had made two calls in recent months to smugglers in Libya, but only to reach relatives being smuggled by those men. Members of the Eritrean diaspora are often forced to be in regular contact with Libya-based smugglers in order to pay the ransoms of their relatives.

To prove his innocence, Berhe gave the passwords and usernames of his social media accounts to Italian prosecutors on Friday, his lawyer, Michele Calantropo, said.

“My client said he is innocent,” Calantropo told the Guardian following the hearing. “There are no elements that [suggest] he is lying. And I firmly believe in his innocence. We’ll try to get him out from jail as soon we can.”

Berhe’s identity documents were allegedly taken by the Sudanese authorities, but his family has supplied school and medical certificates that confirm his name and likeness.

The disclosure risks becoming a major embarrassment for both Italian and British police, who had both confidently announced the news on Wednesday that they had tracked down alleged smuggling kingpin Medhanie Mered at a safe house in Khartoum, Sudan, and then had him extradited to Europe.

Britain’s National Crime Agency hailed the capture of “one of the world’s most wanted people smugglers”, proudly noting how the arrest “was only possible thanks to substantial cooperation between the Sudanese national police and the NCA”.

But on Friday, the NCA went to ground, declining to respond to 12 questions about how the arrest had turned into a case of allegedly mistaken identity.

The NCA would not answer concerns raised by Berhe’s friends and family, as well as Mered’s former victims, that they had arrested the wrong person. They also refused to say what proof they had for the suspect’s identity, beyond the word of the Sudanese government, whose president is wanted for war crimes.

A spokesperson simply said that “we are confident in our intelligence”, and would not expand on why they referred to a “Mered Medhanie” while the Italians consistently call him “Medhanie Mered”.

Prosecutors in Palermo, where the Italian investigation was based, have been more forthcoming, admitting on Thursday to the “unusual” nature of the situation. Following the session on Friday, Maurizio Scalia, Palermo’s deputy chief prosecutor, confirmed that he would investigate concerns over the alleged mistaken identity.

“The suspect was very collaborative and he answered all the questions,” Scalia said. “He admitted he made some calls to Libyan traffickers. We’ll continue to lead appropriate investigations about his identity.”

On Friday, Berhe’s family expressed shock at the prospect of their brother being accused of running a Libyan-based smuggling ring. “It’s not true,” said Seghen, his 30-year-old sister. “He has never been to Libya.”

Earlier in the week, people who said they had been smuggled by the real Mered in Libya said they did not recognise the man extradited to Rome. “I know [Mered] very well, I can recognise him very well,” said Anbes Yemane, a 23-year-old Eritrean student who said he had been smuggled to Italy by Mered in December 2013. “That wasn’t him.”

Hundreds of thousands of Eritreans have passed through Sudan and then Libya on their way to Europe in recent years, fleeing a government that the UN accused this week of committing crimes against humanity on its own people. Many pay thousands of dollars to alleged smugglers, who often torture them in order to exact more payment from their relatives. Hundreds are also believed to have died of thirst and exhaustion in the Sahara as they try to cross into Libya.

Berhe’s family said their relative was just a simple refugee who fled Eritrea in late 2014 – long after Mered is alleged to have begun his smuggling business. Unlike many of his countrymen, however, his family said Berhe stayed put in Sudan while he tried to find a safer route to the west than the hellish route through the Sahara and across the Mediterranean.