Image copyright AFP Image caption Donald Trump was widely criticised for his attack on civil rights hero John Lewis

The number of Democratic members of Congress saying they will boycott Donald Trump's inauguration on Friday has increased to 26.

Many have cited as a reason the president-elect's recent attack on civil rights icon and fellow congressman John Lewis.

Mr Trump lashed out at Mr Lewis on Twitter on Friday after Mr Lewis said he was not a "legitimate president".

He said that Mr Lewis was: "All talk, talk, talk - no action or results."

Mr Lewis was a prominent member of America's civil rights movement and is a hero to many Americans. He was among those beaten by police during the infamous Selma-Montgomery voting rights march of 1965.

As Americans celebrate Martin Luther King Day, the children of the slain civil rights leader - a contemporary of Mr Lewis - have spoken out about the spat.

Martin Luther King III played down the row following a meeting with Mr Trump in New York that he described as "very constructive".

He said that in the heat of the moment "a lot of things get said on both sides".

But his sister Bernice King told a church audience in Atlanta that "God can triumph over Trump".

Media playback is unsupported on your device Media caption John Lewis tells Americans to continue to speak out against hate in MLK day address.

Mr Lewis joined the House of Representatives in 1987 and has served Georgia's fifth congressional district, which Mr Trump went on to call "crime-infested", ever since.

The president-elect's insults, made just days ahead of Martin Luther King Day, were the final straw for a number of Democrats, who will break with tradition by missing the inauguration ceremony on Friday.

"When you insult Rep John Lewis, you insult America," said Yvette Clarke, one of five representatives for New York who will boycott the event. There are 535 members of Congress, across both houses.

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California representative Ted Lieu said: "For me, the personal decision not to attend Inauguration is quite simple: Do I stand with Donald Trump, or do I stand with John Lewis? I am standing with John Lewis."

Illinois representative Luis Gutierrez was the first member of Congress to say he would boycott the inauguration - announcing his decision in December.

"I could not look my wife, my daughters, or my grandson in the eye if I sat there and attended, as if everything that the candidate said about the women, the Latinos, the blacks, the Muslims, or any of those other things he said in those speeches and tweets, and that all of that is OK or erased from our collective memory," Mr Gutierrez told the House.

He has said he will attend the alternative Women's March on Washington the following day.

Image copyright AP Image caption Representative Katherine Clark (centre) is among those who will boycott the ceremony

Mr Lewis's announcement of his own boycott in an interview with NBC News, in which he said that Mr Trump was an illegitimate president, prompted the outburst from the president-elect.

Mr Trump's inauguration will be the second not attended by Mr Lewis in his 30 years in Congress.

The Georgia congressman cited alleged Russian interference in the election among his reasons for regarding Mr Trump as illegitimate.

He also did not attend George W Bush's inauguration in 2001.

"You cannot be at home with something that you feel that is wrong," he told NBC News.

Sales of Mr Lewis's memoir soared to the top of Amazon's US best-seller list following Mr Trump's attack, eventually selling out completely.

Media playback is unsupported on your device Media caption Democrat lawmaker, Mark DeSaulnier, tells the BBC why he is boycotting Trump's inauguration

Mr Lewis led a sit-in protest at the House of Representatives in July to demand a vote on gun control legislation, in the wake of the deadly Orlando shooting.

Republicans adjourned the House early to try to quash the sit-in, switching off the TV cameras, but the C-Span network picked up live streams from some Democrats' phones.

Media playback is unsupported on your device Media caption The moment congressman John Lewis asked Democrats to take action

Katherine Clark, a representative for Massachusetts, was among the first to join Mr Lewis for the gun control protest. Ms Clark said last week she would skip Mr Trump's inauguration.

"Families in my district are fearful that the anti-woman, anti-immigrant, anti-Muslim and divisive promises that drove the Trump campaign will become the policies affecting the health and safety of every American," she said in a statement.

"I do not feel that I can contribute to the normalisation of the president-elect's divisive rhetoric by participating in the inauguration."

Mr Trump has struggled to book any established musicians to perform at his ceremony, despite his team appearing to have cast a wide net.

The event will feature Jackie Evancho, a 16-year-old America's Got Talent contestant, alongside military bands and the Radio City Rockettes, although some members of the Rockettes troupe have publicly refused to take part.

Country music stars including Toby Keith will play a concert on the eve of the inauguration.

Update 23 January 2017: This story has been updated following confirmation from John Lewis's office that he also missed Mr Bush's inauguration ceremony in 2001.