The president's great-uncle, Charles Payne, was part of the 89th Infantry Division which helped to liberate Ohrdruf, one of 88 sub-camps of Buchenwald. Ohrdruf was the first camp freed by American troops.
On Wednesday, the Iranian president Mahmoud Ahmadinejad addressed 600 international academics in Tehran and reiterated his denial of the Holocaust.
He said: "The identity of the liberal democracy has been exposed to the world by its protection of the most criminal regime in the history of humanity, the Zionist regime, by using the big deception of the Holocaust."