US and Iranian fans mingled on trains and buses for the journey to the World Cup match between the two geopolitical foes in Doha on Tuesday.

If there was one thing they had in common, it was the view for one game at least there should be "no politics."

Crowds with the Stars and Stripes and the red, green and white colours of Iran mixed together as they entered the Al Thumama Stadium for the game which both teams need to win if they are to progress to the knockout phase of football's global showpiece.

Iran's team have been under intense scrutiny in Qatar, their players watched for signs they are or are not showing support for mass anti-government demonstrations back home, sparked by the death of 22-year-old Mahsa Amini in morality police custody on September 16.

Al Curtis from Chicago said he had made an effort to speak to Iranian fans. "The whole world sympathises with them but we have to win this game," he said.

"I asked them about the protests and it sounds quite grim."

Seyed Mohammed, a 31-year-old Iranian who lives in Qatar, said: "I can't deny it, this is a special and very sensitive match.

"I don't want to get into politics but it's true that given the events in Iran, a victory would bring joy to the people."

Another Iranian fan, wearing face paint and a wig and with a flag over his shoulders told an AFP reporter it was "dangerous" to be talking to westerners.

"Even if you are only talking about football, no-one will believe you," he said.

Many Iran supporters wore t-shirts proclaiming "Iran France Coupe du Monde 98", a reference in French to the countries' previous meeting at the 1998 World Cup, which ended in a famous victory for the Iranians.

Instead the stadium, the noise from the American fans was fierce with air horns blaring during the Iranian anthem but falling silent for the Star Spangled Banner.

The Iran players had opted not to sing their national anthem before their first match of the World Cup, a 6-2 defeat to England, in an apparent sign of support for the demonstrators at home.

They did sing before their second game, a 2-0 win against Wales that set up the crunch game against the USA and on Tuesday, among the din in the stadium, some of the team mouthed the words without apparent enthusiasm.