U.S. Vice President Kamala Harris's National Security Adviser Nancy McEldowney is stepping down from her role and will be succeeded by her deputy Philip Gordon, according to an internal staff memo seen by Reuters.

Both McEldowney and Gordon have worked for Harris since she took office and have advised the vice president and President Joe Biden on topics such as Afghanistan, Iran, Ukraine, and cybersecurity.

They accompanied Harris on several foreign trips to Central America, Asia and Europe, and have played a key role in shaping her strategy outside the United States.

In the memo to staff, McEldowney said she is stepping down to "focus on some pressing personal matters" but will remain an ardent advocate for Harris and the Biden administration.

"This was a difficult decision because I am so deeply committed to the work we do and the crucial national interest we serve. But after more than a year, this is the right decision for my family," she said. She also noted she's "not rushing out the door" but said the date of her last day was not immediately clear.

A senior administration official said no date has been set yet but it is likely to be at the end of the month.

In her 31-year career as a diplomat in the U.S. Foreign Service, McEldowney has held several roles including ambassador to Bulgaria, and deputy chief of mission in both Azerbaijan and Turkey.

Gordon, a veteran of the Obama and Clinton administrations, currently serves as special assistant to the president and deputy national security adviser to the vice president. He has been involved in all interagency policy discussions, foreign leader meetings and trips, a senior administration official said.

McEldowney's departure comes at a critical time for Harris, who has taken a central role in rallying Western nations and other allies to act against Russia's attack on Ukraine and has increasingly found herself in the middle of high-stakes diplomacy with leaders around the world.

It also comes after a series of high profile exits from Harris's communications team, which had a turbulent first year marked by several messaging failures.

Harris told Reuters in a statement that McEldowney had provided "invaluable counsel" and that she is grateful for her "service - her exceptional talent, deep expertise, and leadership navigating complex challenges."

Gordon, Harris said in the statement, has been a trusted adviser since she took office and brings a wealth of foreign policy experience and knowledge to the role.

White House national security adviser Jake Sullivan told Reuters in a statement that McEldowney "has been a great partner to me and the National Security Council since we took office," and has helped strategize and execute policies around the world with clarity and devotion. Sullivan said he has worked closely with Gordon and knows he will be a "thoughtful and dedicated advisor to the Vice President and all of us."

In other changes to Harris's national security team, Dean Lieberman joined her office in early February as a special advisor for national security and her foreign policy speechwriter - a new role in her office.

He was previously a strategic communications director at the White House National Security Council and served as a spokesman on China, Asia, and Europe, and also supported Harris's foreign policy work.