A man once described by an FBI agent as the world's largest "facilitator" of child pornography will remain held in U.S. custody after his extradition from Ireland, a federal magistrate ruled Wednesday.

A federal public defender representing Eric Eoin Marques, 33, told U.S. Magistrate Judge Timothy J. Sullivan in Maryland that his client isn't currently challenging his detention, but reserves the right to seek bond later. A preliminary hearing for Marques is scheduled for April 8.

A criminal complaint accuses Marques of operating a web hosting service on the darknet that allowed thousands of users to view and share more than 1 million images of child pornography, including violent sexual abuse of prepubescent children.

The darknet is part of the internet but hosted within an encrypted network. It is accessible only through anonymity-providing tools, such as the Tor browser.

Marques, a dual citizen of the U.S. and Ireland, has remained in custody since his August 2013 arrest in Dublin after an extradition request from the U.S.

During a 2013 bail hearing for Marques in Dublin, FBI Special Agent Brooke Donahue described him as "the largest facilitator of child porn on the planet," according to an article posted Saturday on Irish broadcaster RTE's website. Donahue also testified that Marques had been searching online for information about obtaining a Russian visa and citizenship, RTE reported.

"He was trying to look for a place to reside to make it most difficult to be extradited to the United States," the FBI agent said.

Marques, who arrived in the U.S. last Saturday, fought his extradition for years. Irish authorities didn't charge him with any related crimes.

"That decision was made notwithstanding that (Marques) had offered to plead guilty to at least some of the potential charges that might have been brought against him in Ireland," a justice on the Supreme Court of Ireland wrote in March 20 judgment rejecting his final appeal.

Marques hasn't been indicted by a U.S. grand jury or entered any pleas. The charges in his criminal complaint include conspiracy to advertise child pornography and distribution of child pornography.

The complaint said he was suspected of operating a free, anonymous web hosting service on a network allowing users to access websites without revealing their IP addresses. In July 2013, according to the complaint, FBI agents in Maryland connected to the network and accessed a child pornography bulletin board with more than 7,700 members and more than 22,000 posts.

Agents downloaded more than 1 million files from another website on the network, nearly all of which depicted sexually explicit images of children, the complaint said.