WASHINGTON, Aug 17 (Reuters) - Elon Musk, the world's richest person, tweeted on Wednesday that he was joking when he said that he was going to buy English soccer club Manchester United Plc (MANU.N).

"No, this is a long-running joke on Twitter. I'm not buying any sports teams," Musk said, when asked by a user if he was serious about buying the club.

About four hours earlier, Musk had tweeted: "I'm buying Manchester United ur (sic) welcome," without offering any details. Some Manchester United fans, disgruntled by their club's declining fortunes of late, had previously urged Musk on Twitter to consider buying the club.

The tweet turnaround comes as Musk seeks to exit a $44 billion agreement to buy Twitter (TWTR.N) only four months after announcing on the platform he would buy the social media company, which has taken him to court.

Musk has a history of being unconventional and posting irreverent tweets, making it difficult sometimes to tell when he is joking.

"Next I'm buying Coca-Cola to put the cocaine back in," he tweeted on April 27, two days after Twitter's board accepted his unsolicited offer to buy the company.

Musk's tweets about potential acquisitions have landed him in hot water with U.S. regulators in the past.

In 2018, he tweeted that there was "funding secured" for a $72 billion deal to take Tesla private, but did not move ahead with an offer. Musk and Tesla each paid $20 million civil fines - and Musk stepped down as Tesla's chairman - to resolve U.S. Securities and Exchange Commission (SEC) claims that Musk defrauded investors.

The SEC did not immediately respond to a request for comment on Musk's tweet that he was buying the club outside usual business hours.

Musk's ambitions range from colonising Mars to creating a new sustainable energy economy, and in the process he has built the most valuable car company in the world, electric vehicle maker Tesla, rocket company SpaceX, and a slew of smaller firms. One is a tunnel maker called the Boring Company.

Manchester United is one of the most famous names in world soccer but is currently in crisis on the field amid angry calls from fans for the club's current owners, the American Glazer family, to pull out.

The northern England-based team has more than 32 million followers on its main Twitter account and Musk's first tweet about the club had garnered nearly 400,000 'likes' on the platform within four hours.