UN calls for US immigration 're-think' for World Cup

A record 48 teams and millions of fans are descending on the United States, Canada and Mexico for the first World Cup co-hosted by three nations and the largest and most logistically complex ever staged.

But the refusal of US immigration authorities to allow Somali referee Omar Artan, one of Africa's leading match officials, into the country underlined fears that US President Donald Trump's immigration policy could leave deep scars on the tournament.

"I hope that the issues around racial profiling, around... immigration enforcement are not going to affect this World Cup in the way that they have already," Turk told reporters.

"I really hope that there's a massive re-think of how immigration enforcement is impacting human rights and human dignity, and that especially for the World Cup, there is a re-think of the policies that we have unfortunately seen prevailing, especially in the US.

"I also hope that the dehumanisation of the other, the dehumanisation of migrants, the dehumanisation of refugees and asylum seekers is put to an end, because nobody benefits from divisive and polarising narratives."

The World Cup starts at Mexico City's Estadio Azteca on Thursday, with Mexico taking on South Africa, launching a sprawling, nearly six-week-long spectacle that will culminate in the final in New Jersey on July 19.

The US-Israel war on Iran has also loomed large over the tournament.

Iran, who will play three group games on American soil, were forced to switch their training base to Mexico due to the conflict.

The Iranian football federation on Tuesday said its allocation of tickets for fans had been revoked, while some of the team's support staff have been denied visas, in a move Iranian authorities have condemned as "deliberate and discriminatory".