WASHINGTON - Longtime US lawmaker John Lewis doesn't plan to attend President-elect Donald Trump's inauguration next week, saying he doesn’t believe Trump is a "legitimate president."

"I believe in forgiveness. I believe in trying to work with people. It will be hard. It's going to be very difficult. I don't see this president-elect as a legitimate president,” Congressman Lewis said in an interview for NBC News's "Meet the Press."

Lewis, an Afro-American civil rights leader who marched with Martin Luther King Jr, was brutalised by Alabama police during the 1965 “Bloody Sunday” demonstration in Selma for voting rights.

His remark came when asked if he would “forge a relationship” with the president-elect. When pressed on why he believes Trump’s presidency is illegitimate, Lewis pointed to intelligence reports of Russian interference in the election.

“I think the Russians participated in helping this man get elected. And they helped destroy the candidacy of Hillary Clinton,” Lewis said.

Trump acknowledged this week that Russia was responsible for some hacking during the campaign, though the president-elect and many on his team assert that it didn't affect the result of the presidential election.

Lewis also told NBC News that he wouldn’t attend the inauguration, making him the sixth House Democrat to publicly vow not to attend the Jan 20 event.

Congressman Raúl Grijalva (D-Ariz.) announced earlier Friday from the House floor that he plans to skip the event, joining Democratic Congressmen Luis Gutiérrez, Jared Huffman, Katherine Clark and Barbara Lee (Calif.).

“I don't plan to attend the inauguration. It will be the first one that I miss since I’ve been in Congress,” Lewis said. “You cannot be at home with something that you feel that is wrong, is not right.”

Meanwhile, Trump lashed out the civil rights icon and lawmaker. "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," Trump said in a tweet.

"All talk, talk, talk - no action or results. Sad!" he added.

At least eight House Democrats have publicly stated they will not be attending Trump's swearing-in at the US Capitol next Friday, with several indicating their absence will be an act of political protest.