The ceremony, at historic Arlington National Cemetery across the Potomac River from Washington, is also the first time Harris has been seen in public since her November 6 speech in which she conceded the presidential election to Donald Trump.

Democrats, facing a painful reckoning over their drubbing, have begun soul-searching internal discussions -- and some not-so-private blaming -- over what caused Harris's loss, with some pointing to Biden's initial insistence on running again at age 81, despite having promised to be a bridge president to the next generation.

Criticism of Harris herself has been more muted, and Biden heaped praise on Harris last Thursday in a televised White House address.

Earlier Monday Biden hosted veterans at the White House to mark the holiday before heading to Arlington, the final resting place of two presidents, generals from all major US wars, and thousands of other military personnel.

Biden and Harris, both dressed in dark suits, placed their hands on their hearts before participating in a wreath-laying ceremony at the Tomb of the Unknown Soldier.

The president was to deliver remarks at the cemetery's Memorial Amphitheater.

The ceremony comes ahead of Biden hosting Trump at the White House on Wednesday.

The Republican has begun naming loyalists to his new administration. He announced he is bringing a hardline immigration official, Tom Homan, back into the fold to serve as his so-called "border czar," and rightwing congresswoman Elise Stefanik to be US ambassador to the United Nations.

Trump himself has long claimed he is a fierce supporter of America's military, but he has made a series of controversial comments about veterans.

His longest-serving White House chief of staff, retired general John Kelly, has said the Republican leader privately disparaged US servicemembers, including describing those who died or were imprisoned defending America as "suckers" and "losers."

Trump denies the accusation.

But the soon-to-be 47th president has been on record expressing contempt for late American war hero and senator John McCain, who spent years in a Hanoi prison during the Vietnam war.