The United States Soccer Federation temporarily displayed Iran's national flag on social media without the emblem of the Islamic Republic as a show of solidarity with protesters in Iran ahead of the two teams' World Cup clash on Tuesday.
A now-deleted graphic of the Group B standings posted on Saturday across U.S. Soccer's official Twitter, Instagram and Facebook accounts displayed the Iranian flag only bearing its green, white and red colours.
Iran has been gripped by protests since 22-year-old Mahsa Amini's death in September while in police custody after she was arrested for flouting the country's strict Islamic dress code.
The intent of the posts was to show "support for the women in Iran fighting for basic human rights", U.S. Soccer media officer Michael Kammarman told a news conference on Sunday. Players were not consulted on the decision to alter the flag.
"We didn't know anything about the posts but we are supporters of women's rights, we always have been," U.S. defender Walker Zimmerman said.
"We're focused a lot on Tuesday and the sporting side as well... but at the same time we're firm believers in women's rights and support them.
"And we know that it's a lot of difficulties and a lot of heartbreak and in a very disturbing time."
The banner on U.S. Soccer's Twitter page was also changed on Saturday to feature the flag without the emblem. It was changed back 24 hours later to the banner they had been using during the tournament.
Iran's state-affiliated Tasnim News Agency said the Iranian Football Federation will file a complaint against U.S. Soccer to the FIFA Ethics Committee for "disrespecting the national flag" of the Islamic Republic.
Iranian leaders have accused the United States and other foreign adversaries of fomenting the protests in which Iranians from all walks of life have mounted one of the boldest challenges to the theocracy since the 1979 Islamic Revolution.
Washington has imposed sanctions on Iranian officials over the crackdown on protesters. Activist news agency HRANA said 450 protesters had been killed as of Nov. 26, including 63 minors, and over 18,000 have been arrested.
Iran's players declined to sing the national anthem in their first game against England in an apparent show of solidarity with protesters. They sang quietly on Friday before their 2-0 win over Wales, where boos and jeers were heard from Iran supporters.
"We can't speak for them and their message. We know that they're all emotional," Zimmerman said. "They're all going through things right now, they're human. Again, we empathise with that human emotion and completely feel for them."
The United States and Iran will face off in a decisive Group B clash with their place at the World Cup on the line, in a match which was already freighted by decades of enmity between the nations.
With England sitting top of Group B with four points and facing bottom side Wales in their final group game on Tuesday, the Iran-U.S. contest will determine which team goes through to the last 16.
Their eagerly awaited meeting is a rematch of the 1998 World Cup group stage contest - which Iran won 2-1 - when relations between the two nations had also been hostile.