What appears to be the Iranian oil tanker Adrian Darya 1 off the coast of Tartus, Syria - Reuters

Two British-Australian women have reportedly been arrested and detained in Iran amid growing tensions between London and Tehran.

One of the women, a blogger who was travelling through Asia with her Australian boyfriend, was arrested 10 weeks ago on charges which remain unclear, according to The Times.

She was detained by the Iranian Revolutionary Guard for camping in a military precinct around Jajrood in Tehran province, BBC Persia reported

The other woman, an academic who had been lecturing at an Australian university, has been given a 10-year sentence, The Times reported, citing a source with knowledge of the cases.

While the charges against her also remain unclear, 10-year terms are routinely given in Iran for spying charges, the paper reported.

The pair are believed to have been incarcerated in Evin Jail, Tehran, where 41-year old Nazanin Zaghari-Ratcliffe is being held.

The mother of one is a British-Iranian national who has been imprisoned in the country since 2016.

The latest incidents are thought to be the first time British passport holders who do not have Iranian nationality have been imprisoned in Tehran in recent years.

The Foreign Office reportedly requested that the women remained anonymous. The Australian government is taking the lead on both cases.

Australia's Foreign Affairs Department confirmed the arrests but declined to provide details about the cases, citing privacy concerns.

"The Department of Foreign Affairs and Trade is providing consular assistance to the families of three Australians detained in Iran. Due to our privacy obligations, we will not comment further," the department said in a statement.

DFAT on Monday updated its travel advice for Iran. It remains at a level of 'reconsider your need to travel', with the highest level ('Do not travel') applying in some parts of the country.

The blogger and her boyfriend had been documenting their travels on YouTube and Instagram.

Concerns were raised by their online followers when they failed to add any news posts in the past several weeks.

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Tulip Siddiq, who is Mrs Zaghari-Ratcliffe’s Labour MP, told The Times: “This terrible news shows a clear escalation of Iran’s hostage diplomacy. Soft diplomatic responses to Iran’s illegal and inhumane treatment of British prisoners have been a failure.”

The Foreign Office declined to comment. It states on its website: “There is a risk that British nationals, and a higher risk that British-Iranian dual nationals, could be arbitrarily detained in Iran. All British nationals should consider carefully the risks of travelling to Iran.”

The news came as Britain accused accused Tehran of an "unacceptable" breach of international norms after it apparently broke a promise that an oil tanker detained off Gibraltar this summer would not deliver oil to Syria.

Dominic Raab, the Foreign Secretary, summoned the Iranian ambassador on Tuesday afternoon following reports that the Adrian Darya 1, which was at the centre of a diplomatic crisis after being seized by Royal Marines in July, had delivered a cargo of crude oil to the Syrian port of Tartus.

Britain says Iran repeatedly gave assurances that the ship would not deliver oil to any EU-sanctioned entity in Syria or elsewhere before it was released last month.

Mr Raab said: “Iran has shown complete disregard for its own assurances over Adrian Darya 1.

“This sale of oil to Assad’s brutal regime is part of a pattern of behaviour by the Government of Iran designed to disrupt regional security. This includes illegally supplying weapons to Houthi insurgents in Yemen, support for Hezbollah terrorists and most recently its attempts to hijack commercial ships passing through the Gulf.

“We want Iran to come in from the cold but the only way to do that is to keep its word and comply with the rules-based international system.”

The Adrian Darya 1, known as the Grace 1 until it was renamed by its owners last month, was seized by Gibraltar authorities and Royal Marine Commandos acting on intelligence that it was bound for Syria on July 4.

Britain and Gibraltar said the move was to enforce European Union sanctions that forbid the supply of oil to the regime of Bashar al-Assad, the Syrian dictator.

It was released in August after a court in Gibraltar accepted assurances that the vessel would not breach the sanctions, and rejected a last-minute US bid to have it impounded.

But the vessel spent several days meandering near the Syrian coast and turned off its transponder before apparently making its delivery last week.