Australia's foreign minister said she has demanded Iran free three Australian citizens from a Tehran prison as she revealed she held one-to-one talks on the issue with her Iranian counterpart last week.
"The government has been making efforts to ensure they are treated fairly, humanely and in accordance with international norms," Marise Payne said, adding that there was "no reason" to believe the arrests were politically motivated.
Perth-based Jolie King and Mark Firkin had been documenting their journey from home to Britain on social media for the past two years but went silent after posting updates from Kyrgyzstan and Pakistan about 10 weeks ago.
Analysts and family members of dual nationals 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.
Relatives appeals for a change of heart in Tehran.
"Our families hope to see Mark and Jolie safely home as soon as possible," a statement released on behalf of their relatives said.
Before setting off, the couple had written on their blog that they "can't wait to share all of our experiences and the beauty of all the different destinations and countries we will be visiting".
News of the arrests came after Australia's conservative government announced it would contribute a frigate and surveillance aircraft to a US-led mission to protect shipping through the Strait of Hormuz, with tensions high in the Gulf region.
But Ms Payne said the detention of the couple and a third person – reported to be a British-Australian female academic – was not related to broader global issues.
"We have no reason to think that these arrests are connected to international concern over Iran's nuclear program, United Nations sanction enforcement or maritime security of the safety of civilian shipping," she said.
Already difficult relations between Iran and US allies have threatened to boil over since President Donald Trump in 2018 abandoned a deal to curb Tehran's nuclear programme, and Iran resumed proscribed nuclear activities.
Ms King, who is being held in Tehran's Evin prison, had been told she was being held as part of a plan to facilitate a prisoner swap, according to reports..
Nazanin Zaghari-Ratcliffe, a British-Iranian project manager with Thomson Reuters Foundation, has been held in Tehran since 2016 on sedition charges, a case that has caused major tensions with the United Kingdom.
According to Richard Ratcliffe, his wife has described Ms King as "scared" by her experience of solitary confinement.
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.
Iran has demanded a prisoner swap to bring Negar Ghodskani, 40, back home. She was arrested in Australia at the request of US authorities and gave birth in prison in Adelaide.
After she was extradited in July, she pleaded guilty to the charge of conspiracy to export prohibited technology to Iran, which carries a sentence of up to five years in a federal US prison.
"Let’s have an exchange. I’m ready to do it. I have the authority to do it," said Iran's Foreign Minister Mohammad Javad Zarif in April.
The arrests also come as Australia's Prime Minister Scott Morrison agreed to a US-led military effort to protect ships passing through the Strait of Hormuz.
Meanwhile on Friday, France, Germany, the UK and the European Union expressed their "deep concern" over Iran's "announcements and actions in contradiction with its commitments under the" 2015 nuclear deal.
The four heavyweights said they "believe the latest developments underline the need for diplomatic efforts towards de-escalation and resumption of dialogue, which we fully support."
