Trump called Mattis "the most overrated general" after the former US defense secretary said the White House boss divided the country.

"The only thing in common between me and Barack Obama is the honor of firing Jim Mattis, the most overrated general in the world. I ask him to resign and feel great about that.

The White House boss said that the main strength of former US defense secretary Jim Mattis is not in the ability to run the army but to build a personal image.

"I bring a new life to him, with battles to win, but he rarely brings results. I don't like the leadership style or anything of Mattis and many agree.

The remarks came after General Mattis criticized the White House boss for not having "mature leadership," referring to Trump's reaction to protests that are rife throughout the United States today.

"Donald Trump is the first President I see not trying to unite the American people, not even pretending to try to do it. Instead, he is trying to divide us. We are witnessing the consequences."

The former Pentagon leader also opposed the decision to use force to disperse protesters outside the White House earlier this week for Trump to go to a nearby church.

Jim Mattis was nicknamed "Mad Dog" because of his remarkable battle achievements and rare fighting spirit.

Mattis was fired by former President Barack Obama from the position of commander of US Central Command in 2013. After being elected in 2016, Trump praised Mattis as a "true general" and nominated him to hold the post.