LONDON — In 2017, Jolie King and Mark Firkin hit the road in a white Toyota Land Cruiser, beginning a journey that over the next two years would take them from their home in Perth, Australia, across large stretches of Asia as they meandered toward Europe.
Photos and videos posted on social media accounts documenting their adventure show the pair swimming in the turquoise waters of Bali, trekking to Everest base camp and driving through the valleys of Pakistan surrounded by snow-capped peaks.
Then, at the end of June, their posts suddenly stopped.
On Thursday, officials confirmed that the couple were among three Australian citizens detained in Iran for the past 10 weeks. Rights groups have expressed concerns that they may have been tortured, and a fellow prisoner’s husband reported that Ms. King had been held for weeks in solitary confinement.
It is unclear why the pair were detained, and the Iranian authorities have not responded to requests for comment about Ms. King and Mr. Firkin. Pouria Zeraati, a prominent Iranian journalist, said the pair had been detained after flying a drone near Tehran without a permit.
Their arrest came at a time of rising animosity between Tehran and the West. Since the United States withdrew from a landmark 2015 deal offering Iran incentives to restrict its nuclear development, and reimposed damaging sanctions, the two sides have exchanged a series of provocations and Iran has repeatedly detained tankers in the Persian Gulf, a crucial region for the transport of global oil supplies.
Australia’s Department of Foreign Affairs said in a statement that it was providing consular assistance to the families of all three Australians detained in Iran, and released a statement from the families of Ms. King and Mr. Firkin.
“Our families hope to see Mark and Jolie safely home as soon as possible,” they said, offering no further comment and asking for privacy.
Ms. King is a dual citizen of Australia and Britain. The Times of London, which first reported the detentions on Wednesday, said that a British-Australian academic had also been detained in Iran, though it did not disclose her name.
The British Foreign Office declined to speak about individual cases, but noted in a statement that Dominic Raab, Britain’s foreign secretary, had met with the Iranian ambassador on Wednesday and “raised serious concerns about the number of dual national citizens detained by Iran and their conditions of detention.”
The British Foreign Office advises people with both British and Iranian citizenship not to travel to Iran, citing a risk of arrest, but it considered the risks to non-Iranians as limited.
Australia warns its citizens against unnecessary travel to Iran, citing a risk of arbitrary detention or arrest, particularly for those whom the Iranian authorities deem to be attracting attention.
Some have raised concerns that the Australian detainees might be used by the Iranian government as leverage for a prisoner swap.
Mohammad Javad Zarif, Iran’s foreign minister, publicly proposed a prisoner exchange with the United States in April, and raised the cases of Nazanin Zaghari-Ratcliffe, a British-Iranian dual citizen, and an Iranian woman being held in Australia. Iran has detained several non-Iranians and people with Iranian citizenship in recent years, including at least four Americans.
“We have an Iranian lady in Australia who gave birth to a child in prison,” Mr. Zarif said in a discussion at a research institute in New York, adding that the case involved the purchase of transmission equipment for an Iranian broadcasting company.
Ms. King and the other Australian-British woman are being held at Evin Prison in Tehran, a notorious facility where Ms. Zaghari-Ratcliffe has been detained for years.
Ms. Zaghari-Ratcliffe’s husband, Richard Ratcliffe, said Ms. King was being held in the same facility as his wife — whom he is in regular contact with — and that Ms. King had recently been released from solitary confinement.
Mr. Ratcliffe described how prisoners can often spend weeks in solitary confinement, as his wife did, before being transferred to the political ward. He said that although prisoners are sometimes allowed to make domestic calls and have visits from immediate family members behind a glass screen, he was unsure whether Ms. King had been able to speak to her family.
He described the conditions in solitary confinement as harrowing, with the prisoner confined to a room the size of a double bed, with no bed, no window or natural light, and just a few blankets.
Ms. King and Mr. Firkin had been documenting their journey, which they named The Way Overland, on social media and a website, living out of their car as they trekked from country to country.
Many of the videos posted on their social media accounts feature drone photography and videography of the landscapes they passed through, and they had used crowd funding to support their adventure in recent months.
“We both share a great love for being outdoors and an appreciation for the happiness that putting yourself outside of your comfort zones brings you,” they wrote on the “About Us” section of the website dedicated to their journey.
Their time frame was open ended, but they had planned to arrive in Britain by Christmas. Their Toyota was topped with a pop-up tent, where they often slept while on the road.
“Hopefully we can stretch this trip out as long as possible, as it’s only so often between life’s commitments that we get the chance to spend this much time exploring,” they wrote on their website.
But some of their thousands of followers became concerned as the silence grew longer and days turned into weeks.
“You guys ok? It’s been awhile!” one Instagram user wrote.
“I hope everything is okay since there hasn’t been an update for a while,” wrote another.
By Thursday morning, as news of their arrest spread, those messages had turned to calls for their release.
One of their Instagram followers posted an emoji of praying hands and a simple message: “Hope you both are safe and can make it back on the road soon.”