Potential talks with North Korea were apparently the catalyst for booting Rex Tillerson from the State Department.
A senior White House official told reporters President Donald Trump "wanted to make sure to have his new team in place in advance of the upcoming talks with North Korea and various ongoing trade negotiations."
Last week, Trump accepted an invitation to meet with North Korean leader Kim Jong-un by May.
But the same day, Tillerson told reporters negotiations with the North were still a far off.
"We're a long way from negotiations," Tillerson said. "We just need to be very clear-eyed and realistic about it."
As of Tuesday morning, a meeting between Trump and Kim hadn't been scheduled.