The US authorities have charged 80 people, “most of whom are Nigerians,” with participating in a conspiracy to steal millions of dollars, prosecutors say.
They are accused of using business email fraud schemes and romance scams to con victims – many of them elderly.
Two Nigerian nationals, identified as Valentine Iro and Chukwudi Christogunus Igbokwe, who are part of those arrested in the US, have been named as co-conspirators working with others in the US and in Nigeria, to obtain money from victims and then transfer it abroad.
They managed to fraudulently obtain $6m (£5m) in a conspiracy aimed at stealing $46m, the US Attorney’s Office alleges.
The remaining 66 defendants are believed to be abroad, “with most them located in Nigeria”, the authorities say.
Those named should be handed to the US to face a trial, Abike Dabiri-Erewa, who heads the Nigerian government’s diaspora commission said in a statement.
“We ask those accused in Nigeria to voluntarily turn themselves in to American authorities to clear their names, without which the Nigerian government should extradite them if relevant international treaties between the two governments are invoked.”
The actions of a few should not tarnish all Nigerians, she added.
Police have so far arrested 14 suspects across the US, 11 in Los Angeles alone.
Others are thought to be in Nigeria and authorities there say they will cooperate with US.
Prosecutors say it is one of the “largest cases of its kind in US history”.
The FBI investigation is a major step to disrupt criminal networks, US Attorney Nick Hanna said.
“This case is part of our ongoing efforts to protect Americans from fraudulent online schemes and to bring to justice those who prey upon American citizens and businesses,” he added.
The FBI started investigating the case in 2016 in a single bank account but it later extended to cover multiple victims in the US and around the world.