WASHINGTON (REUTERS) - Vice-President Kamala Harris' senior adviser and chief spokesman, Ms Symone Sanders, is leaving by the end of the year, marking the latest high-profile departure from her office amid growing concerns over messaging and how well Ms Harris is being positioned for future roles.

Ms Sanders worked for President Joe Biden for nearly three years, and often travelled with Ms Harris on domestic and foreign trips.

She worked with the Vice-President as she navigated complex issues such as voting rights in the United States and fixing root causes of migration from Central America's Northern Triangle countries.

"V-P values Symone and she is beloved... grateful to have her through the end of the year," said a White House official, who did not wish to be identified, confirming her departure.

Earlier this month, Ms Ashley Etienne, Ms Harris' communications director, also left the administration.

A separate White House official familiar with the situation said the departures come amid concerns that Ms Harris is not being adequately prepared or positioned, and instead is being sidelined.

Messaging challenges have been a constant struggle for Ms Harris' office through the first year of this administration.

In June, she was grilled during an interview by an NBC anchor over why she had not visited the US-Mexico border despite being put in charge of the nation's migrant crisis.

This was followed by a woman, who claimed to be a reporter, who made her way into the Vice-President's news conference in Mexico. More recently, Ms Harris' first in-studio interview was scuttled after anchors on the show tested positive for Covid-19 at the last minute.

Ms Sanders, who did not respond to a request seeking comment, sent a note to staff on Wednesday (Dec 1) announcing her decision.

"From my first days on the President's campaign to travelling with the V-P when she joined the ticket, to witnessing the historic swearing in of the President and Vice-President. It's been an honour," she said.