Trump writes longest-ever social media post to slam comedian Bill Maher

US President Donald Trump has lashed out at American comedian Bill Maher just days after praising him following their White House dinner.

In his longest-ever social media post, the 80-year-old Republican president called the comedian a "complete and total loser", accusing the HBO host of lying about their recent meeting and his approval ratings.

According to Factba.se, which tracks Trump's social media activity, the 1,322-word message was his longest among more than 97,000 posts published since 2011.

The attack came after Maher, 70, discussed his October 15 dinner with Trump during Friday's episode of Real Time, where he made jokes about the president's popularity and claimed their meeting lasted four hours.

Trump, however, disputed the comedian's account, saying the dinner lasted two hours or less and that he had learned nothing from the conversation.

He also claimed Maher appeared drunk during the meeting, looked nervous and repeatedly sought an invitation to the White House through his associates.

Interestingly, Trump had described the same dinner as "great" just days earlier, telling reporters that Maher liked him more than people realised.

The dinner was also attended by musician Kid Rock and sports commentator Stephen A. Smith, who separately said they had spent more than four hours at the White House.

Trump also accused Maher of using a "laughter machine" to make his jokes appear funnier and questioned his claims about the president's approval ratings.

The president further revealed that he was considering relocating journalists from their existing White House workspace, but denied having any plans to turn the press briefing room into a swimming pool.

He concluded the lengthy post by telling Maher not to contact him again and declaring that he would never watch his television programme again.