Milad Panahipour, an Iranian lawyer, said Parastoo Ahmadi, 27, was arrested in Sari City, capital of the northern province of Mazandaran, on Saturday.
On Thursday, the judiciary had filed a case regarding Ahmadi’s concert performance, in which she performed wearing a long black sleeveless and collarless dress, but no hijab. She was accompanied by four male musicians.
Ahmadi had posted her concert online the day before, saying: “I am Parastoo, a girl who wants to sing for the people I love. This is a right I could not ignore; singing for the land I love passionately.”
The online concert has been viewed more than 1.4 million times.
Panahipour said: “Unfortunately, we do not know the charges against Ms Ahmadi, who arrested her, or her place of detention, but we will follow up on the matter through legal authorities.”
He also said two musicians in Ahmadi’s band – Soheil Faghih Nasiri and Ehsan Beiraghdar – were arrested in Tehran on Saturday.
Under rules imposed after the 1979 Islamic revolution, women must cover their hair in public and are also not allowed to sing alone in public.
Ahmadi has built a wide following among Iranians for songs posted on her Instagram page, including audio clips and videos of ballads sung indoors without a headscarf supporting the 2022-2023 mass protests against the authorities.
The protests were sparked by the death in custody of 22-year-old Mahsa Amini, after her arrest in Tehran for an alleged breach of the Islamic republic's strict dress code for women.
Wednesday's video stream appears to be the first time that Ahmadi has recorded a full concert outside, as opposed to the more intimate recitals filmed indoors.
A written message on the YouTube video before the concert starts says: "I am Parastoo, the girl who cannot remain silent and refuses to stop singing for the country she loves."
She tells viewers to "listen to my voice in this imaginary concert and dream of a free and beautiful nation".
In one the songs, she sings in apparent reference to deadly crackdowns in 2022-2023 and on other protests in Iran: "From the blood of the youth of the homeland, tulips have grown."
Social media users praised the striking quality of the almost half-hour video, which was streamed live from an unspecified location.
- 'Shook a nation' -
Without naming Ahmadi, the Mizan Online news website of the Iranian judiciary said Thursday "a group led by a female singer" had performed "music without observing legal and religious standards".
The judiciary has "intervened and taken appropriate action, with a legal case filed against the singer and the production staff," it added.
US-based dissident campaigner Masih Alinejad hailed the concert as "historic", saying on social media that "her voice is a weapon against tyranny, her courage a song of defiance".
Prominent commentator Karim Sadjadpour, a fellow with the US-based Carnegie Endowment for International Peace, described the concert as an "act of extraordinary courage" that marked "another crack in the foundations of Iran's rotting theocracy".
"Parastoo Ahmadi shook an entire nation," said the France-based Iranian women's rights collective Association Femme Azadi.
"Iranian women are the greatest resistance fighters of our time."
The streaming of the concert took place ahead of a new law expected to come into force on Friday that rights groups have warned will drastically increase the penalties on women deemed to have flouted the dress code.
Amnesty International said in a report Tuesday that women could even face the death penalty if convicted under the "Promotion of the Culture of Chastity and Hijab" law.
"This shameful law intensifies the persecution of women and girls for daring to stand up for their rights," said Diana Eltahawy, Amnesty's deputy director for the Middle East and North Africa.
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