Washington (CNN) President Donald Trump has told advisers that Heather Nauert, the State Department spokeswoman, is his leading choice to become US ambassador to the United Nations and he could offer the post as soon as this week, two sources familiar with his pick told CNN.

If named Nauert, who met with Trump Monday, would leave her role at the State Department to take over from Nikki Haley, who surprised White House officials last month when she announced her decision to step down at the end of the year.

People close to the President cautioned that his pick is not final until it is formally announced. The White House declined to comment on the matter. Nauert has been keeping a low profile this week after meeting with Trump on Monday. Two of her daily briefings have been conducted by her deputy.

Speaking at the White House on Thursday, Trump confirmed that Nauert is "under very serious consideration" to become the next US ambassador to the UN.

"She's excellent. She's been with us a long time. She's been a supporter for a long time. And she's really excellent," Trump said.

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