The gesture ahead of the team's Asian Cup match against South Korea last week was widely seen as an act of defiance against the Islamic republic just two days after the United States and Israel attacked it.

The son of Iran's late shah, US-based Reza Pahlavi, warned on Monday that the refusal to sing the anthem could have "dire consequences", and urged Australia to offer the team protection.

Trump weighed in later, pressing Australian Prime Minister Anthony Albanese to "give ASYLUM" to the team and adding: "The US will take them if you won't."

"Australia is making a terrible humanitarian mistake by allowing the Iran National Woman's Soccer team to be forced back to Iran, where they will most likely be killed," the US leader said on his Truth Social network.

Pahlavi, who has not returned to Iran since before the 1979 Islamic revolution that ousted the monarchy, has billed himself as the man to lead a democratic transition to a secular Iran as the theocratic regime fights to survive.

"The members of the Iranian Women's National Football Team are under significant pressure and ongoing threat from the Islamic Republic," he said on social media.

"I call on the Australian government to ensure their safety and give them any and all needed support."

Politicians, human rights activists and even "Harry Potter" author J.K. Rowling have also called for the team to be offered official protection.

"Please, protect these young women," Rowling said in a post on social media.

- 'Save our girls' -

In response to their refusal to sing, a presenter on Iranian state television branded the side "wartime traitors".

Crowds banged drums and shouted "regime change for Iran" as they gathered outside the Gold Coast stadium where the side played their last match over the weekend.

They then surrounded the Iranian team bus, chanting "let them go" and "save our girls".

On Monday, an AFP journalist saw members of the team speaking on phones from their balcony of their hotel.

Canberra has so far declined to comment on whether it could offer the players asylum.

Asked about their case on Sunday, Foreign Minister Penny Wong said Australia "stands in solidarity" with the people of Iran.

A spokesperson for Australia's Home Affairs department told AFP it "cannot comment on the circumstances of individuals".

Amnesty International campaigner Zaki Haidari said they faced persecution, or worse, if they were sent home.

"Some of these team members probably have had their families already threatened," Haidari told AFP.

"Them going back... who knows what sort of punishment they will receive?"

Despite being heavily monitored, the side would have a "small window of opportunity" to seek asylum at the airport, he said.

Iran's embassy in Australia did not respond to a request for comment.