The "first puppy" is a six-month-old black-and-white Portuguese water dog that the Obama girls have named Bo, the Washington Post reports.

The girls - Malia, 10, and Sasha, 7 - were promised a puppy by their father, US President Barack Obama, as a reward for coping with the election campaign.

The identity of the puppy - which had been one of Washington's best kept secrets - will be officially revealed by the White House on Tuesday afternoon, the Post said.

They said young Bo - who sports a white chest, white paws and a white goatee - was a gift to the Obama daughters from close family friend, Democratic Senator Edward Kennedy of Massachusetts.