WASHINGTON -- FBI Director Robert Mueller told Congress on Wednesday that bringing Guantanamo Bay detainees to the United States would pose a number of possible risks, even if the they were kept in maximum-security prisons. 

During his appearance Wednesday before the House Judiciary Committee, Mueller was asked what concerns the FBI has about the prospect of transferring to the United States some of the 240 inmates currently held at the naval base in Cuba. 

President Barack Obama has ordered the Guantanamo Bay detention center closed by January 2010, but that timetable may be in jeopardy. Congress is seeking to block any funding for bringing any detainees to the U.S., whether freed or imprisoned. 

At the start of Wednesday's hearing, Mueller was asked what concerns the FBI has about the release of Guantanamo detainees. 

"The concerns we have about individuals who may support terrorism being in the United States run from concerns about providing financing, radicalizing others," Mueller said, as well as "the potential for individuals undertaking attacks in the United States." 

"All of those are relevant concerns," Mueller said. 

The FBI chief said he would not discuss specific individuals. He said there were also potential risks to putting detainees in maximum security prisons. 

Rep. Jerrold Nadler, D-N.Y., whose district includes the World Trade Center site, then prodded Mueller to agree that such individuals could be safely kept in maximum security prisons in the U.S. 

Mueller balked at Nadler's suggestion, noting that in some instances imprisoned gang leaders have run their gangs from inside prisons. 

"It depends on the circumstances," Mueller said. 

Republicans have been attacking Obama on the issue, and even fellow Democrats say they need to see a plan for closing Guantanamo before they can support the White House on it. 

Republicans urged Mueller to take the FBI's concerns to the White House. 

"No good purpose is served by allowing known terrorists, who trained at terrorist training camps, to come to the U.S. and live among us," said Rep. Lamar Smith of Texas, the senior Republican on the committee. "Guantanamo Bay was never meant to be an Ellis Island."