White House spokeswoman Sarah Sanders said Trump and Haley would meet in the Oval Office at 10:30 am (1430 GMT), while the president tweeted he would be making a "Big announcement with my friend Ambassador Nikki Haley."

Trump's UN envoy since January 2017, Haley's resignation was reported by US media including CNN, Fox News and The New York Times -- none of which gave a reason for her departure.