United States and Spanish authorities said on Friday Michael Pratt, a fugitive since 2019, was arrested by Spanish police in Madrid on Wednesday pursuant to an Interpol "Red" notice - a request to track down a person for prosecution or to serve a sentence.
The 40-year-old New Zealander is charged with "sex trafficking, production of child pornography, sex trafficking of a minor and conspiracy to launder monetary instruments in connection with the operation of (an adult) website", FBI San Diego said.
According to authorities, between 2012 and 2019 Pratt and others allegedly recruited young women, including minors, to engage in commercial sex acts by force, fraud and coercion.
Online pornography websites owned and operated by Pratt and an accomplice generated more than $US17 million ($A25 million) dollars in revenue, according to the FBI.
Pratt, who was added to the FBI's Ten Most Wanted Fugitives List earlier this year, is being held in Spain pending extradition, the FBI said.
"The capture of Michael Pratt is an example of how the FBI will pursue justice beyond US borders - you can run but you can't hide," FBI special agent Stacey Moy said.
The FBI had offered a reward of up to $US100,000 ($A148,810) for information leading to his arrest.
According to Spanish police, who didn't name the New Zealander, the capture marked the first time someone on the FBI's most wanted list was arrested in the country.
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