WASHINGTON (AFP)---US President Barack Obama on Friday said "never forget, never again," as he remembered six million Jews and others killed by the Nazis and marked International Holocaust Remembrance Day.   

"We commit ourselves to keeping their memories alive not only in our thoughts, but through our actions," Obama said in a written statement.  

"As we remember all those who perished in camps from Auschwitz to Treblinka, Dachau to Sobibor, we pledge to speak truth to those who deny the Holocaust."  

Obama pledged to celebrate the resilience of Holocaust survivors and to stand strong against those who commit modern-day atrocities and against what he said was "the resurgence of anti-Semitism."  

"Together with the State of Israel, and all our friends around the world, we dedicate ourselves to giving meaning to those powerful words: 'Never Forget. Never Again.'"   

Mitt Romney, the front-running Republican candidate who Obama could meet in November's presidential election, also issued a statement.  

"On this day, we pause to remember the millions of Jews murdered in Europe.  But it is not enough merely to reflect on those horrors and the evil that brought it about.   

"At a moment when the state of Israel is under threat from violent terrorists, from tyrants seeking nuclear weapons, and from a campaign to deny the legitimacy of a Jewish state, the United States must stand shoulder to shoulder with our ally in its quest for peace and security."   

Romney and other Republican candidates have accused Obama of watering down strong US support for Israel, but the White House says the president has done more than any other administration to protect the Jewish state.