U.S. Department of Homeland Security Secretary Kirstjen Nielsen visits U.S. President Donald Trump's border wall in the El Centro Sector in Calexico, California, U.S. October 26, 2018. REUTERS/Earnie Grafton

WASHINGTON (Reuters) - U.S. President Donald Trump has decided to replace Homeland Security Secretary Kirstjen Nielsen, but has not settled on the timing, the Wall Street Journal reported on Tuesday, citing unidentified White House and administration officials.

Nielsen is a close ally of White House Chief of Staff John Kelly and her firing might prompt Kelly to quit, the Journal reported. Trump is aware of that possibility and said he probably would replace Kelly with Nick Ayers, who is currently chief of staff to Vice President Mike Pence, it reported.