There are 241 inmates at the facility at Guantanamo Bay, Cuba, and Holder spent the past several days privately asking European leaders in London, Prague, and Berlin for help relocating detainees the United States wants to set free.
Before the speech, Holder met with reporters, saying the United States has made decisions on a group of about 30 detainees, but has not yet decided where it wants to send them.
He said the United States is weeks away from asking certain countries to take detainees.
"We have about 30 or so where we've made the determination that they can be released. So we will . . . be reaching out to specific countries with specific detainees and ask whether or not there might be a basis for the moving of those people from Guantanamo to those countries," Holder said.
The previous Bush administration had approved about 60 detainees for release, and Holder aides would not say whether the 30 he was referring to were part of that group. Additionally, about 20 detainees have been ordered released by the courts, though their cases remain unresolved.
President Obama has ordered the controversial detention site shuttered in the next nine months and has assigned Holder to oversee that effort.
Holder said he has been telling European officials over the past week that the problem the order to close created "is best solved by a unified response."
Closing Guantanamo is good for all nations, he argued, because anger over the prison has become a powerful global recruiting tool for terrorists.
