The Justice Department says it has sent a Guantanamo detainee to France, and another to Hungary.
The transfers immediately followed the hand-over of two other detainees to Italy to face trial on terrorism charges.
The United States sent Saber Lahmar to France. In 2008, a U.S. judge had ordered him released from Guantanamo, after originally being held on suspicion of plotting to attack the U.S. Embassy in Sarajevo.
Another man, a Palestinian, was sent to Hungary, but U.S. officials would not identify him.
The four transfers to European nations leave 211 detainees still at the detention center. Since 2002, more than 500 detainees have been released.