The United States and Iran meet in a politically charged winner-takes-all World Cup clash on Tuesday as England aim to reach the last 16 as group winners with victory over Wales.

Ever since the draw for the tournament was made in April, the Group B game between the US and Iran has stood out as one of the highlights of the first phase in Qatar.

Even with little riding on the result, the game at Thumama Stadium would have been loaded with political overtones, only the third meeting on a football field of two nations who share more than 40 years of ideological enmity.

But Tuesday's match carries an additional dimension with both teams knowing that a win will see one of them advance to the knockout rounds while the loser is eliminated.

As if that wasn't enough, simmering tensions flared up at the weekend after the US Soccer federation posted a modified version of the Iranian flag on their social media feeds.

The move infuriated Iranian football chiefs, who lodged a complaint with world governing body FIFA demanding sanctions.

US Soccer initially said the altered flag was intended as a gesture to show support for women protesters in Iran, before subsequently deleting the various posts.

Coach Gregg Berhalter said on Monday his players and team staff had been in the dark about the flag gesture and sought to de-escalate tensions by emphasising that politics would not be a factor on Tuesday.

"When I think about this match I know that a lot of other constituents have a lot of other feelings towards it," Berhalter said.

"But for us it's a soccer game against a good team and it's not much more than that. It's a knockout game between two good teams that want to get to the next round."

Iran counterpart Carlos Queiroz brushed off suggestions that the flag furore would be used to motivate his players.

"If after 42 years in this game as a coach I still believe I can win games with those mental games, I think I've learned nothing about the game," the Portuguese coach said.

- Wales need miracle -

In Tuesday's other Group B game England will be looking for a win over Wales as they bid to qualify for the last 16 as group winners.

England made a flying start to the tournament with a 6-2 demolition of Iran but were then held to a 0-0 draw by the USA in a laboured performance.

England manager Gareth Southgate is expected to tweak his starting line-up to rest some of his star men against a Welsh team who need a miracle to qualify.

In other games on Tuesday, the Netherlands face already eliminated hosts Qatar as the Dutch strive to finish top of Group A.

Ecuador, who are level with the Dutch on four points, will finish top of the group if they come up with a better result against Senegal than the Netherlands manage against Qatar.

The winners of Group A will face the runners-up from Group B in the last 16. Failure to top the group could conceivably see the Netherlands face England in the second round.

Holland manager Louis van Gaal is unfazed by whoever his team meets in the next round.

"If you want to become world champions you have to be capable of beating anyone," van Gaal said.