An Iranian woman who was arrested in Tehran last month for apparently protesting peacefully against the country's mandatory Islamic dress code has been freed, a human rights lawyer says.

"The girl of Enghelab Street has been released," lawyer Nasrin Sotoudeh wrote in a post on her Facebook page on January 28.

A video showing the woman, whose name has not been made public, standing on a concrete structure on Tehran’s Enghelab (Revolution) Street without wearing a head scarf, a punishable offense in Iran, went viral on social media after December 27.

She was silently waving a white flag in an apparent protest against the compulsory hijab, which in Iran refers to Islamic dress that covers the hair and body.

Sotoudeh said she had gone to the prosecutor's office to follow up the case and learned of her January 27 release from detention.

"I hope they don't fabricate a legal case to harm her for using her basic rights," the lawyer said. "She has not done anything wrong to deserve prosecution."

Sotoudeh wrote on her Facebook page last week that the woman is a 31-year-old mother of a toddler. The lawyer also said she was initially released after being detained on the spot but was subsequently rearrested.

Iranian authorities have made no public comment on the case.

The woman has become a symbol of defiance against the strict dress code enforced in Iran.

Thousands of social media users have asked about her whereabouts through the hashtag #Where_is_she or #Whereisthegirlfromenghelabstreet.

In a January 24 statement, Amnesty International called on Iranian authorities to “immediately and unconditionally” release the woman.

The London-based rights group also reiterated its calls on the authorities to “end the persecution of women who speak out against compulsory veiling and abolish this discriminatory and humiliating practice.”

Women's dress has been heavily scrutinized in the Islamic republic since the 1979 revolution, when adherence to an Islamic dress code became compulsory.

The dress code dictates that women's hair and body must be covered in public.

Morality police launch regular crackdowns on those who are not fully respecting rules relating to the hijab.