Both announcements were made after Trump agreed this month to meet with North Korean leader Kim Jong-un to discuss the regime's denuclearization.

In dismissing Tillerson, an advocate for engagement with Pyongyang, Trump reportedly wanted a top diplomat who was more in line with his views and named Central Intelligence Agency Director Mike Pompeo to the role.

Pompeo has made hawkish statements about the North Korean regime, as has Bolton.

The former ambassador represented the US at the UN from 2005-2006 and served as under secretary of state for arms control and international security from 2001-2005. At the time, he made a series of remarks highly critical of the regime in Pyongyang and then-leader Kim Jong-il. He also called for a regime change in Pyongyang.

The North unleashed vituperation in response, describing him as "human scum," "devoid of reason," "an ugly fellow who cannot be regarded as a human being" and a "bloodthirsty fiendish bloodsucker," among other things.

McMaster, an Army lieutenant general, said in a statement he will be retiring from service this summer.

Trump said in a separate statement that McMaster's leadership of the National Security Council helped his administration bolster America's national security.

"He helped develop our America First National Security Strategy, revitalize our alliances in the Middle East, smash ISIS, bring North Korea to the table and strengthen our nation's prosperity," the president said. "This work and those achievements will ensure that America builds on its economic and military advantages."

A White House official noted on background that the departure had been discussed for some time.

"The timeline was expedited as they both felt it was important to have the new team in place, instead of constant speculation," the official said, referring to Trump and McMaster. "This was not related to any one moment or incident, rather it was the result of ongoing conversations between the two." (Yonhap)