White House chief of Staff John Kelly (R) walks with Kirstjen Nielsen, the chief of staff at the Department of Homeland Security, on the South Lawn of the White House in Washington, US, before his departure with President Donald Trump to Yuma, Arizona, August 22, 2017. [Photo/Agencies]

WASHINGTON - US President Donald Trump will nominate Kirstjen Nielsen, an aide to White House chief of staff John Kelly, to be Homeland Security secretary, media reports said on Wednesday.

The announcement was expected to be made as soon as later in the day, according to US news outlet Politico.

Nielsen, 45, currently serves as the deputy White House chief of staff. She was Kelly's top aide when the former four-star Marine general led the Department of Homeland Security (DHS) during the early months of the Trump administration.

She moved to the West Wing with Kelly who was appointed in July after former White House chief of staff Reince Priebus was pushed out.

An expert on national and cyber security, Nielsen enjoys an extensive background in homeland security missions, including stints at the Transportation Security Administration and on the White House Homeland Security Council under former President George W. Bush.

Elaine Duke is running the DHS on an interim basis. If Nielsen's appointment is confirmed by the Senate, she would become the first former employee to run the department established after the terrorist attack on September 11, 2001.

Nielsen holds degrees from the Georgetown School of Foreign Service and the University of Virginia Law School.