Iran's only female Olympic medalist has announced she is defecting in a blistering online letter in which she described herself as "one of the millions of oppressed women" in the country.

Taekwondo champion Kimia Alizadeh, who won a bronze medal at the 2016 Rio Olympics, criticised Iran's political system in a social media post on Sunday, accusing the country's authorities of using her as a propaganda tool.

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The 21-year-old implied in an Instagram post written in Farsi that she had moved to Europe but her location is unknown. Iran's semi-official ISNA news agency reported earlier this month that Alizadeh had emigrated to the Netherlands.

"No one has invited me to Europe and I haven't been given a tempting offer. But I accept the pain and hardship of homesickness because I didn't want to be part of the hypocrisy, lies, injustice and flattery," she said.

Alizadeh said the Islamic Republic's authorities had attributed her success to their management and the fact that she wore a headscarf, which is obligatory for women in Iran.

"I am one of the millions of oppressed women in Iran whom they've been playing for years ... I wore whatever they told me and repeated whatever they ordered. Every sentence they ordered I repeated," she wrote.

"None of us matter for them, we are just tools."

Alizadeh added that while the government exploited her sporting success politically, officials would humiliate her with remarks such as "It is not virtuous for a woman to stretch her legs!"

Mahin Farhadizadeh, a deputy Iranian sport minister, said he had not read Alizadeh's post but that he believed she "always wanted to continue her studies in physiotherapy", ISNA reported.

Alizadeh said at the time of her medal win in the 57kg category that it had made her happy for Iranian girls. However, in her post on Sunday, she appeared torn by her decision.

"Should I start with hello, goodbye or condolences? Hello oppressed people of Iran, goodbye noble people of Iran, my condolences to you people always mourning," she wrote.

In the past week, 176 people, many of them Iranians with dual citizenship, were killed when the Iranian military mistakenly shot down a Ukrainian airliner on Wednesday.

Also on Wednesday, at least 56 Iranians died in a stampede at the funeral for military commander Qassem Soleimani, who was killed in a US air strike.

Officials would humiliate Alizadeh by saying it was not virtuous for a woman to stretch her legs, she said [File: Issei Kato/Reuters]

In her post on Sunday, Alizadeh said she wanted nothing more than "taekwondo, security and a happy, healthy life".

Alizadeh is the third top Iranian sports person to stop representing the country in recent months.

In December, Iran's chess federation said top-rated chess champion Alireza Firouzja had decided not to play for Iran over the country's informal ban on competing against Israeli players.

Three months earlier, the International Judo Federation said Iranian judoka Saeid Mollaei had refused to return home over fears for his safety after he ignored orders from his national federation to pull out of fights to avoid a potential final meeting with an Israeli opponent.