Britain's National Crime Agency (NCA) says it is aware of the claims following an international operation to capture one of the world's most-wanted people smugglers.
Known as "The General," Mered Medhanie, 35, was arrested and extradited to Italy
after being accused of being a key smuggler of people from Africa to Europe.
However, friends of the arrested man say his identity has been mistaken.
A spokesperson for the NCA told CNN it was aware of the reports: "This is a complex multi-partner operation and it is too soon to speculate about these claims."
Despite the claims, the NCA is "confident in its intelligence gathering process," it said.
Friends on Facebook have named the extradited man as Medhanie Tesfamariam and claim he is innocent.
Medhanie was arrested in Sudan after the NCA tracked his address in the country's capital Khartoum.
It is also believed he is responsible for the October 2013 shipwreck off the Lampedusa coast
in which more than 300 asylum seekers, mostly from Eritrea, drowned in sight of the Italian Island.
"Medhanie is a prolific people smuggler and has absolute disregard for human life," Tom Dowdall, deputy director of the National Crime Agency, said in a statement.
"Medhanie no doubt thought he was beyond the reach of European justice but we were able to support the Italians by tracking him down to Sudan," he said.
Italian authorities had intercepted telephone conversations to confirm Medhanie was coordinating trips on the Mediterranean to Europe, the NCA said.
In one conversation, Medhanie "was heard laughing about the fatal overloading of migrant ships," the agency said.
More than 2,500 migrants have died
while attempting to cross into Europe this year.