Australia's Department of Foreign Affairs and Trade said it was providing consular assistance to the families of all three. The department said it could not comment further due to privacy obligations.
A British-Australian blogger and her Australian boyfriend were detained 10 weeks ago while traveling through Asia, The Times newspaper in London reported.
A British-Australian academic who studied at Cambridge University and was lecturing at an Australian university was detained separately and sentenced to 10 years in prison, the newspaper reported. The newspaper said she was being held in solitary confinement but it did not know what she had been convicted of doing.
The lecturer has been behind bars for almost a year, Australian Broadcasting Corp. reported.
The Australian government, the newspaper and the ABC have not released names.
The three are held in Tehran's Evin prison, where British Iranian Nazanin Zaghari-Ratcliffe, 41, has been detained since 2016 on spying charges, the newspaper reported.
The women are thought to be the first British passport holders who do not also have Iranian nationality to have been imprisoned by Tehran in recent years, the newspaper said.
The blogger was being held in the same ward for female political prisoners as Zaghari-Ratcliffe, the newspaper reported.
Iranian authorities told the blogger she was being held as part of a plan to facilitate a prisoner swap with Australia, the newspaper said, citing an anonymous source with knowledge of the cases.
The couple were in Iran as part of a trip that started in Australia three years ago, the paper reported.
ABC reported the two cases were not connected.
There was no immediate comment Wednesday from Iranian officials, nor state media. Cases involving dual nationals typically end up in closed-door hearings of Iran's Revolutionary Court, where former detainees say they had no opportunity to defend themselves against spying charges or offer evidence.
Analysts and family members of dual nationals and others detained in Iran long have said hard-liners in the Islamic Republic's security agencies use the prisoners as bargaining chips in negotiations with the West. A U.N. panel in 2018 described "an emerging pattern involving the arbitrary deprivation of liberty of dual nationals" in Iran, which Tehran denied.
A prisoner exchange in January 2016 that freed Washington Post journalist Jason Rezaian and three other Iranian-Americans also saw the U.S. make a $400 million cash delivery to Iran the same day, which involved money from a weapons sale in the era of the late Shah Mohammad Reza Pahlavi.
Several British nationals with Iranian backgrounds are similarly held as Iran and Britain have been discussing the possible release of some 400 million pounds held by London since the 1979 Islamic Revolution for a tank purchase that never happened.
It's unclear what Australia would offer in return, though the 2016 prisoner swap saw Iranians held in the U.S. similarly released. Several Americans remain held in Iran now as well.
Detentions of those with Western ties have spiked in the past around sensitive times in Iran. Tensions between Iran and the U.S. remain high over Tehran's unraveling 2015 nuclear deal with world powers, which President Donald Trump unilaterally withdrew America from over a year ago. Recently, Iran has broken the deal's limits on enrichment, its uranium stockpile and the use of advanced centrifuges, trying to pressure Europe to offer it a way to sell its crude oil on the international market despite U.S. sanctions.
Australia has advised its citizens to "reconsider your need to travel" to Iran, the highest warning on a four-tier scale after "do not travel" to a country.
Britain and Australia last month signed onto a U.S.-led maritime security mission to protect international shipping in the Strait of Hormuz, where Iran's recent seizures of vessels has raised tensions with the West.
Associated Press writer Jon Gambrell in Dubai, United Arab Emirates, contributed to this report.