The imprisoned British-Australian academic Kylie Moore-Gilbert has begged the Australian prime minister to secure her release from an Iranian jail, as human rights groups urge foreign governments to take a stronger line with Tehran.

A Cambridge-educated academic specialising in Middle East politics, Moore-Gilbert has been imprisoned in Tehran’s notorious Evin prison since September 2018, after she was arrested at Tehran airport while trying to leave the country after attending an academic conference.

Moore-Gilbert, who holds both British and Australian citizenship but was travelling on her Australian passport, was arrested by the intelligence arm of Iran’s Revolutionary Guard Corps, having been flagged as “suspicious” by a fellow academic. She was tried and convicted in secret last year on charges of espionage and sentenced to 10 years in prison. An appeal against her sentence failed.

Last June, Moore-Gilbert wrote to the prime minister: “I beg you to act faster to bring this terrible trauma that myself and my family must live through day after day.” In the letter, smuggled out of prison, and published by the Centre for Human Rights in Iran, she said she had travelled to Iran on a university program for foreign academics, “as well as naively to conduct some research interviews”.

“Unfortunately, one of my academic colleagues on this program and one of my interview subjects flagged me as suspicious to the Revolutionary Guards.”

Moore-Gilbert has been held in the high-security unit of the Revolutionary Guards’ own prison within Evin, including months in solitary confinement. There, she has been confined to a 2mx3m cell, where the lights remain on 24 hours a day. She is blindfolded if she is ever taken out of her cell and has almost no contact with the outside world, seeing only her jailers and interrogators. The Guardian understands Moore-Gilbert has been allowed only two visits from Australian consular officials during her imprisonment.

On Christmas Eve, she wrote again: “Six months have passed … during this time I have remained in the same prison without any improvement in my intolerable conditions.

“Over the past nine months I have been completely banned from any contact with my family, with the exception of a three-minute phone call (with my father), which was only granted after I took desperate measures which put my own life at risk.

“I have undertaken five hunger strikes as my only means to raise my voice, but to no avail. As predicted, I have now received a conviction of 10 years in prison, and my appeal … has failed.

“I beg of you, prime minister Morrison, to take immediate action, as my physical and mental health continues to deteriorate with every additional day that I remain imprisoned in these conditions.”

The Australian foreign affairs minister, Marise Payne, said the Australian government was working “every day with our agencies here and with counterparts in Iran to … secure Dr Moore-Gilbert’s release”.

“We have had an opportunity for a consular visit towards the end of last year,” she said. “Our view is that we don’t accept the charges upon which she was detained, held, charged and convicted, and we want to ensure the conditions in which she is held are appropriate.”

A spokesman for Iran’s foreign ministry, Abbas Mousavi, said last month that “Iran will not submit to political games and propaganda” in response to media reports of diplomatic pressure.

Moore-Gilbert was detained for “violating Iran’s national security”, Mousavi said. “Like any other individual with a sentence, [she] will serve her time while enjoying all legal rights”.

Jasmin Ramsey, the communications director with the Centre for Human Rights in Iran, said there was very little information about Moore-Gilbert emerging from inside Evin prison but it was believed she remained isolated within the Revolutionary Guard-run high-security section of the prison.

“Kylie’s case is unusual,” she said. “She has been in prison for a long time, she’s been charged and sentenced, and then they threw out her appeal. It’s contrary to Iranian law to keep her in solitary. She should be moved to the women’s ward for political cases but that’s not happened ... She remains isolated and it is, as she described in her letter, a form of psychological torture.”

Ramsey said if Australia’s strategy was to pursue negotiations quietly, “there needs to be a united front: with the Australian government, alongside allies that have leverage on Iran like the EU countries and Japan, telling the [Iranian] government, ‘you can’t take foreign nationals to use as hostages’.”

Tara Sepehri Far, a researcher with Human Rights Watch, said the cases of Moore-Gilbert and other foreign nationals detained in Iran were marked by serious violations of due process.

“Kylie has been detained in the very securitised ward of Evin prison under IRGC supervision and is isolated from her family. She deserves due process and urgent attention of the Australian government.”

Sepehri Far said cases such as Moore-Gilbert’s were rarely resolved through a transparent and fair judicial process.

“There are increasing signs that the Iranian government is willing to use them as incentives in bilateral negotiations, which is very troubling. But this shouldn’t prevent the Australian government from doing its best to assist Kylie.”

Iran’s relationship with the US and its allies is under acute strain. The US assassination of Iran’s most powerful general, Qassem Suleimani, was met last week with missile strikes on US bases in Iraq.

Iran faces internal pressure too: mass anti-government protests have erupted in the capital after the Revolutionary Guards, on high alert for US retaliation, “accidentally” shot down a passenger plane killing 176 people.

Australia has sent HMAS Toowoomba to the Middle East as a contribution to the US-led coalition protecting oil tankers traversing the Strait of Hormuz.

Iran also wants to force western forces from neighbouring Iraq – over which it seeks to impose greater influence – and Australia’s continued commitment to the US coalition there is a further complication in the relationship.

Australia has fewer levers of influence to pull with Tehran. The Iranian citizen Negar Ghodskani, held in an Adelaide prison for two years on allegations of sanctions busting while she fought extradition to the US, was ultimately sent to America where a judge sentenced her to time served and ordered her released. Ghodskani has since returned to Iran.

Two other Australians – the travel bloggers Jolie King and Mark Firkin – held for allegedly flying a drone near a military base in Tehran were released in October reportedly as part of an informal “prisoner swap” for the Iranian doctoral student Reza Dehbashi Kivi, who was imprisoned in Brisbane for more than a year pending extradition to the US over allegations he exported American radar equipment for detecting stealth planes or missiles to Iran.