US President-elect Joe Biden has accused authorities of treating pro-Donald Trump protesters more leniently than anti-racism demonstrators who were forcibly dispersed by police in Washington last year.

Iran Press/America: "No one can tell me that if it had been a group of Black Lives Matter protesters yesterday ... they wouldn't have been treated very, very different than the mob of thugs that stormed the Capitol," Biden said on Thursday.

He admitted, "We all know that's true, and it is unacceptable."

Biden also called the group "domestic terrorists" and laid the blame for the violence squarely at the outgoing president's feet.

He said people should not call the hundreds who broke into the Capitol protesters - rather, he said, they were "a riotous mob - insurrectionists, domestic terrorists".

The images of the crowd racing through the Capitol building on Wednesday stood in sharp contrast to the handling of anti-racism protests near the White House a few months ago.

The White House was surrounded by multiple blocks of buffers, and law enforcement officers used tear gas, projectiles and at one point the downward blast of a helicopter’s rotor to push back protesters separated from the building by rings of fencing.

Vice President-elect Kamala Harris said the world "witnessed two systems of justice" on Wednesday, when "we saw one that let extremists storm the United States Capitol, and other that released tear gas on peaceful protesters last summer."

"We know this is unacceptable, we know we should be better than this," she said on Thursday.

"The challenge we are facing in our country is about more than the actions of the few we watched yesterday. It's about how to reform, how to transform, a justice system that does not work equally for all.

"A justice system that is experienced differently depending on if you're white or black ... rich or poor."