A British-Australian woman jailed in Tehran on espionage charges said she rejected an offer from Iran to become a spy, according to letters she smuggled out of prison.

Kylie Moore-Gilbert, a lecturer in Islamic Studies at Melbourne University, has been in prison since September 2018 and is serving a 10-year term.

In extracts of the letters smuggled out of Tehran's Evin prison and published by British media on January 21, Moore-Gilbert wrote that she is "imprisoned for a crime I have not committed" and fears for her mental health.

The Guardian and The Times newspapers reported that the letters were written in rudimentary Persian language to Iranian officials between June and December 2019.

One letter addressed to her "case manager" read: "Please accept this letter as an official and definitive rejection of your offer to me to work with the intelligence branch” of the Islamic Revolutionary Guards Corps (IRGC).

"I am not a spy. I have never been a spy and I have no interest to work for a spying organization in any country," Moore-Gilbert wrote.

In other letters, she said her health has “deteriorated significantly," having been taken to hospital twice and the jail's infirmary six times.

The academic complained that she has been denied visits and phone calls and has been held in an "extremely restrictive detention ward."

"I think I am in the midst of a serious psychological problem," she said.

Australia has rejected the charges against Moore-Gilbert as entirely false and called for her to be treated "fairly, humanely, and in accordance with international norms."

Last month, Iranian Foreign Ministry spokesman Abbas Musavi said Moore-Gilbert must serve out her sentence and that the country "will not submit to political games and propaganda."

In October, Australian travel bloggers Jolie King and her boyfriend Mark Firkin were released after spending months in an Iranian jail, while Australia freed a jailed Iranian academic, Reza Dehbashi Kivi.

With reporting by The Guardian, Times, and the BBC