Donald Trump conceded that Joe Biden would become US president this month and condemned the “heinous” mob attack on Congress, putting an end to his unprecedented campaign to overturn the results of November’s election.

In an abrupt change of tone on Thursday evening, the president accused violent demonstrators of “defiling the seat of American democracy” and said those who broke the law “will pay”.

His comments in a video posted to Twitter came as Democrats mounted a push to forcibly remove him from office after he came under intense criticism for inciting the assault. The previous day he described rioters as “very special”.

Mr Trump conceded that Congress had completed the certification of the election results and that “a new administration will be inaugurated on January 20”. But he stopped short of congratulating Mr Biden, who he did not mention by name.

“My focus now turns to ensuring a smooth, orderly and seamless transition of power,” said Mr Trump, reading from a teleprompter. “This moment calls for healing and reconciliation.”

He added: “Serving as your president has been the honour of my lifetime.”

The video message followed a day of violent unrest in Washington that interrupted the certification of the election. US Capitol Police said that one of its officers died on Thursday night from injuries sustained “while physically engaging with protesters”, the fifth death resulting from the assault.

“To those who engage in the acts of violence and destruction: you do not represent our country,” Mr Trump said. “And to those who broke the law: you will pay.”