The White House tried to head off a diplomatic spat with Poland after President Barack Obama mistakenly called a Nazi facility used to process Jews for execution as a "Polish death camp."

The linguistic faux pas overshadowed Obama's posthumous award of America's highest civilian honor, the Presidential Medal of Freedom, to Jan Karski, a former Polish underground officer who provided early eyewitness accounts of the Nazi purge against Jews.

"Before one trip across enemy lines, resistance fighters told him that Jews were being murdered on a massive scale, and smuggled him into the Warsaw Ghetto and a Polish death camp to see for himself," Obama said....