The five detainees are Yemeni; four went to Oman, and one to Estonia, apparently. Here's Helene Cooper, of the New York Times:
WASHINGTON — The United States transferred five more detainees — all of them Yemenis — from the military prison at Guantánamo Bay, Cuba, on Wednesday, the Defense Department announced. Their release intensified the dispute between the Obama administration and several Republican senators over President Obama’s recent flurry of transfers as he seeks to empty the American-run prison.
The latest transfers came one day after several Republican senators, including John McCain of Arizona, proposed legislation that would place a moratorium on the release of most of the prisoners held at Guantánamo. The move was widely interpreted as an attempt to halt the recent surge in releases.
The proposed legislation would bar transfers to Yemen for two years and would suspend virtually all transfers from Guantánamo for the same period, repealing the law that has allowed the administration to transfer 33 prisoners in the last year.
The Senators' wrong-headed legislative proposal---about which I hope to say more shortly---can be found here.