After recently moving to resettle a handful of Guantanamo Bay detainees in small island countries, the Obama administration is focusing on the more difficult task of finding larger countries to take prisoners.

Career State Department diplomat Daniel Fried, who is acting as the main U.S. salesman seeking new homes for the detainees, met Wednesday with counterparts in Spain to ask that four detainees be resettled there.

Separately, Attorney General Eric Holder, at a Senate hearing Wednesday, estimated more than 50 detainees could end up on trial by U.S. authorities, as the Obama administration pushes ahead to close the prison amid rising public opposition.

The process of finding new homes for the 229 Guantanamo inmates accelerated in recent days with the transfer of four Chinese Uighurs to Bermuda, and an agreement from the Pacific island nation of Palau to take as many as 13 more of the Chinese-dissident Muslims.

U.S. allies in Europe, Asia, as well as Australia are now the main focus of the U.S.-detainee transfer negotiations.

At the hearing, Holder said he was aware that public sentiment has turned increasingly against the closure of Guantanamo since President Obama signed orders to close the prison and review the individual cases of detainees. Much of the concern arises from the prospect of detainees moved to the U.S. for trial or release, an issue Republicans and some Democrats have raised.

A government official says well over 50 other detainees have been approved for transfer to other countries. Negotiations continue with Saudi Arabia to accept a large group of Yemeni detainees, who represent the largest nationality among remaining prisoners.