Civil rights leader John Lewis urged young people to protest against injustice and to get involved in the democratic process, days after he had been slammed by Donald Trump for being “all talk, no action”.

The Democratic congressman who has been in office since 1986 told the audience at a Martin Luther King Jr memorial breakfast that today’s generation should use social media, their voices and education to make a difference.

“So I say to you as role models, never give up, never give in. Stand up, speak out. When you see something that’s not right, not fair, you have a moral obligation to say something,” he said.

The scars of racism, he said, were still “deeply embedded in society”.

“Yes, we have made a lot of progress as a nation and as a people, but we are not there yet.“

His speech on the national holiday did not mention Mr Trump once, but his words could be interpreted as a subtle shot at the President-elect who had criticised him and his district on social media.

"Congressman John Lewis should spend more time on fixing and helping his district, which is in horrible shape and falling apart (not to mention crime infested) rather than falsely complaining about the election results," Mr Trump wrote on twitter.. "All talk, talk, talk - no action or results. Sad!"

Vice President-elect Mike Pence defended his boss, saying he had a right to defend himself, after Mr Lewis had questioned Mr Trump's legitimacy as President.

"Hate is too heavy a burden to bear," said Mr Lewis, quoting Dr King at the memorial breakfast.

"So I say to the future leaders of this state, the future leaders of this nation, of the world - you must never, ever hate. The way of love is a better way. The way of peace is a better way," he said.

Mr Lewis talked about his long history of activism, which included marching in Selma, Alabama, being beaten by the Ku Klux Klan and arrested by the police.

"I thought it was my last non-violent protest. I thought I was going to die on that bridge," he said.

He also spoke of his humble upbringing in Alabama, where he realised as a child that he wanted to become a preacher, and would "preach to the chickens" in his back yard. He went on to university and met icons such as Rosa Parks.

"We all must become participants in the democratic process," he added.

"When you become old enough to vote, go register and vote. The vote is precious. It is almost sacred. It is the most powerful non-violent tool we have in a democratic society and we must use it."

Clayborne Carson, a history professor at Stanford University and the person selected by Coretta Scott King to edit her husband's letters and papers, told The Independent that Mr Trump's decision to attack Mr Lewis was "idiocy".