Speaking at a summit with EU leaders in Vienna on June 21, Bush said he wants to send the detainees back to their home countries.
But he said that some detainees there are "cold-blooded killers" who must be brought to justice.
Bush also addressed the standoff over Iran's nuclear program. Iran earlier today said it would respond to a international incentives package to give up uranium enrichment by August 22. But Bush renewed calls for Iran to give its answer within "weeks, not months."
"It seems like an awful long time for a reasonable answer, for a reasonable proposal -- a long time for an answer," Bush said. "We look forward to working with our partners. We just got word of this [Iranian] statement as we walked in here, but it shouldn't take the Iranians that long to analyze what is a reasonable deal."
Bush also said that North Korea's apparent plans to test-fire a long-range ballistic missile are "disturbing," and called on North Korea to honor agreements it has made on refraining from missile tests.