Barack Obama visited the Norwegian embassy in Washington on Tuesday to express his condolences to the families of those killed in the terrorist attack last week, dpa reported.
Obama was accompanied by Vice President Joe Biden at the ambassador's residence as each delivered handwritten letters to honour the victims of the "tragic killings," a White House official said.
"To the people of Norway - we are heartbroken by the tragic loss of so many people, particularly youth with the fullness of life ahead of them," Obama's letter reportedly said.
"No words can ease the sorrow but please know that the thoughts and prayers of all Americans are with the people of Norway, and that we will stand beside you every step of the way," it said.
Seventy-six people died in the bombing attack in downtown Oslo and the shootings by the same suspect at a youth camp on Utoya island.