Nigeria, Jan. 27 -- Former FIFA president Sepp Blatter has waded back into global football's biggest political fault line, openly backing calls for fans to boycott World Cup matches in the United States over growing security and civil rights concerns.

Mr Blatter's comments, made on Monday via social media, lend high-profile support to a controversial warning issued by Mark Pieth, the Swiss anti-corruption lawyer who once worked with FIFA on governance reforms during Blatter's presidency.

"I think Mark Pieth is right to question this World Cup," Mr Blatter wrote, aligning himself firmly with calls for supporters to stay away from the United States.

The 2026 FIFA World Cup, set to be hosted jointly by the United States, Canada and Mexico...