WASHINGTON: US Vice-President Kamala Harris on Monday said she is ready to serve and people around her know about "her capacity" to lead.

Harris' remarks gain significance amid questions over the age of President Joe Biden and recent comments by a special counsel about his weak memory, which has been denied by the White House.

"I am ready to serve. There's no question about that," Harris told The Wall Street Journal in an interview.

The financial daily said the interview was conducted two days before the special counsel's report on Biden's handling of classified documents amplified concerns about the 81-year-old incumbent's mental acuity.

The report said Biden displayed "diminished faculties" in interviews and called him an "elderly man with a poor memory".

Everyone who sees her on the job, Harris said, "walks away fully aware of my capacity to lead", according to The Wall Street Journal.

The vice-president, however, described her boss as an "incredible leader", according to a statement released by the Biden-Harris campaign.

"I have been with Joe in the Oval Office when the cameras are there and when they are not. I have watched him bring folks together across the nation and across the world. He is an incredible leader," she said.

Harris said the comments made by the special counsel were unnecessary, inaccurate and inappropriate.

"The way the president's demeanour was characterised in that report could not be more wrong. It was clearly politically motivated," she said.

"When it comes to the role and responsibility of a prosecutor in a situation like that, we should expect a higher level of integrity than what we saw. Nevertheless, I want you to know the Joe that I know," Harris said.