The 89-year-old took to X on Monday to express his support for Pieth's stance, writing: "For the fans, there's only one piece of advice: stay away from the USA! I think Mark Pieth is right to question this World Cup."

Pieth, an anti-corruption specialist who led FIFA's Independent Governance Committee between 2013 and 2016, raised concerns about immigration enforcement and security risks under the Trump administration in an interview with Swiss newspaper Der Bund.

Pieth painted a stark picture of conditions in the United States, describing the country as being "in a state of tremendous turmoil."

"What we're witnessing domestically – the marginalization of political opponents, the abuses by immigration authorities, and so on – doesn't exactly entice a fan to travel there," he told the Swiss publication.

The lawyer drew a striking parallel between American and Mexican security conditions, noting that while drug cartels pose the threat south of the border, the US faces dangers from "a state that's becoming increasingly authoritarian."

He also warned supporters to expect harsh treatment at the border, suggesting that those who displease officials could find themselves "put straight on the next flight home."

The tournament, jointly hosted by the United States, Mexico and Canada, is scheduled to run from 11 June to 19 July, with all knockout matches from the last 16 onwards taking place on American soil.

Blatter's intervention follows the deaths of two US citizens, Renee Good and Alex Pretti, in Minneapolis this month after encounters with Immigration and Customs Enforcement officers, incidents that have triggered widespread unrest across the country.

Supporters from Iran and Haiti already face barriers to attendance, as their nations are among 39 countries whose citizens are currently prohibited from entering the United States.

Blatter served at the helm of world football's governing body for 17 years before being forced from office amid a major corruption scandal that engulfed FIFA in 2015.

Last year, he and former UEFA president Michel Platini were acquitted of charges relating to a two million Swiss franc payment made to Platini in 2011.

FIFA has yet to issue any official response to Blatter's remarks, with preparations for the expanded 48-team competition continuing across all three host nations.

The current FIFA president Gianni Infantino, who succeeded Blatter following the corruption crisis, has maintained a close relationship with President Trump.