NEW YORK -- US President Donald Trump on Thursday nominated his national security advisor Mike Waltz as the next US ambassador to the United Nations.

"In the interim, Secretary of State Marco Rubio will serve as National Security Advisor while continuing his strong leadership at the State Department," said Trump in a post on social media.

Both Waltz and his deputy Alex Wong are expected to leave their current roles in the White House as soon as Thursday, according to earlier media reports.

Waltz's nomination to be US ambassador to the United Nations requires Senate confirmation.

On March 27, Trump withdrew his nomination of Republican Elise Stefanik to be the US ambassador to the United Nations.

Former US Ambassador to the United Nations Linda Thomas-Greenfield left her office on Jan 20 when Trump took office as US president.