US President Barack Obama said in an interview aired on Monday he worried that detainees freed from the US military prison at Guantanamo, Cuba, might resume attacks on the United States.
But he told NBC News that closure of the prison was a matter of upholding US values and law, and that a failure to do so would ultimately make Americans less secure.
"Can we guarantee that they're not going to try to participate in another attack? No," Obama said. "But what I can guarantee is that if we don't uphold our Constitution and our values, that over time that will make us less safe. And that will be a recruitment tool for organisations like Al Qaeda."
In one of the first acts of his new administration, Obama, who was sworn in as US president on January 20, signed an executive order directing that Guantanamo prison be closed within a year.
Some 250 terrorism suspects are being held at Guantanamo, many of them detained for years without charge and some subjected to interrogation that human rights groups say amounted to torture.
Obama critics note that even former President George W Bush wanted to close Guantanamo. They say the difficult issue is deciding what to do with the inmates because they cannot be sent home for fear of torture, and other countries are unwilling to take them.
There also are fears some may return to their attacks against the United States. Several of the detainees released by the Bush administration again became active in anti-US militant groups.
"Is it going to be easy?" Obama asked in the interview. "No, because we've got a couple hundred of hard-core militants that, unfortunately, because of... some problems that we had previously in gathering evidence, we may not be able to try in ordinary courts but we don't want to release."
But he expressed confidence that the administration would ultimately find a solution balancing security and US legal values.
"I have to make the very best judgments I can make in terms of what's going to keep the American people safe and... what's going to uphold our Constitution and our traditions of due process," Obama said. "And what I'm convinced of is – we can balance those interests in a way that makes all of us proud but also assures that we're not attacked."