Australia on Thursday called on Tehran to treat "humanely" three citizens detained in Iran, as it emerged two of those arrested were a travel-blogging couple on an overland trip to Britain.
Foreign Affairs Minister Marise Payne said she had raised the cases "many times" with her Iranian counterpart Javad Zarif, including as recently as last week.
"The government has been making efforts to ensure they are treated fairly, humanely and in accordance with international norms," she 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.
"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 Payne said the detention of the couple and a third person -- reported to be a British-Australian woman and 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.
The Times newspaper in London reported that King, who was being held in Tehran's Evin prison with the other arrested woman, had been told she was being held as part of a plan to facilitate a prisoner swap.
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.
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.
It was not immediately clear if any of the three have been charged.