Alan Liotta, speaking to a roundtable of bloggers, also said another 150 are eligible for release. The remainder -- he did not say how many -- are "too dangerous" to be released but will not be prosecuted.

Some are "just too dangerous to take the chance that if we give him back to another country, they'll let that guy go. And so those guys are the ones that I think we have to look at as being held on the long -- over the long term," Liotta said.

The Pentagon estimates half of all detainees held at Guantanamo Bay Naval Base have already been released from the camp and sent back home.

At least 75 are approved for release but remain at the camp. Their governments have not assured the United States they will be either adequately monitored or treated humanely once they return, Liotta said.

"Some of the countries are willing to take the measures that we see as necessary to mitigate the threat of the detainees when they return back. Some of them are not. And some of the countries are willing to do it, but we have concerns about humane treatment issues. The State Department has concerns about humane treatment issues, and so it prevents us from sending them back," Liotta said.

He blamed "the courts" for blocking the return of some.

"In some cases, we have no problems, everybody's agreed to send them back, and the courts are preventing us to send those guys back," he said.

His comments come as the Bush administration is reportedly discussing ways to close the camp. Defense Secretary Robert Gates is on record as wanting to shut it, and former Secretary of State Colin Powell has called for its termination.