Australia on Wednesday revealed that three of its citizens had been detained in Iran, the latest in a series of Westerners to be seized by authorities in Tehran.
News of the trio's detention comes at a sensitive geopolitical juncture, and after Australia announced that it would join a US-led mission to protect shipping through the Strait of Hormuz with tensions high in the Gulf region.
"The Department of Foreign Affairs and Trade is providing consular assistance to the families of three Australians detained in Iran," a spokesperson told AFP, declining to comment further citing privacy obligations.
Canberra is battling to keep efforts to free the trio under wraps, and it is not clear if the three have been charged.
Confirmation of their detention comes after the Times of London reported that two British-Australian women were being held in Tehran's Evin prison, and Australian broadcaster ABC said that the Australian boyfriend of one of the women was also detained.
One of the women was reported to be an academic who has been in detention for months, while the couple were said to have been detained while camping near a military facility on a journey across Asia.
Earlier this week, the Australian government updated its travel advice for Iran to "reconsider your need to travel" and "do not travel" to areas near the border with Iraq and Afghanistan.
Prime Minister Scott Morrison last month announced a "modest" contribution to the US-led Gulf mission -- including a frigate, a P8 maritime surveillance aircraft and support staff -- which will also involve British forces.
Already difficult relations between Iran and the United States -- and American allies -- have threatened to boil over since President Donald Trump abandoned a deal to limit Tehran's nuclear programme in 2018.
Iran has responded by resuming some proscribed nuclear activities.
- Collateral damage? -
Meanwhile, a rising number of dual nationals have been detained in Iran in what many see as a ruthless diplomatic strategy.
They include Meimanat Hosseini-Chavoshi, an Iranian-Australian population expert who was detained late last year while visiting Iran on a study tour.
Analysts see the arrests as either a tactical ploy to gain diplomatic leverage or as part of the murky politics in Iran -- with hardliners in the judiciary and the security apparatus scuttling the more conciliatory approach of moderates.
The detention of two dual British-Australian citizens, if confirmed, would deepen tensions between London and Tehran and pose a further challenge to embattled Prime Minister Boris Johnson.
The two countries have clashed over Britain's detention of an Iranian tanker, which was released recently on the condition that it did not provide oil to Syria.
"It is now clear that Iran has breached these assurances and that the oil has been transferred to Syria and (President Bashar al-Assad's) murderous regime," the British Foreign Office said Tuesday.
Johnson had previously come in for withering criticism for jeopardised the case of Nazanin Zaghari-Ratcliffe, a British-Iranian woman held in Tehran for sedition, by mischaracterising her job.
"Iran once again ups the stakes" with the latest arrests, said Tulip Siddiq, Zaghari-Ratcliffe's member of parliament.
"This is a wake up call for our Prime Minister, Government and Ministers that they must act urgently to bring our innocent citizens home."