The European Union called on Saturday for the release of Nobel Peace Prize laureate Narges Mohammadi, who was detained by Iranian security forces along with at least eight other activists.
Brussels described Friday's arrests in the eastern city of Mashhad as "deeply concerning".
"The EU urges Iranian authorities to release Ms. Mohammadi, taking also into account her fragile health condition, as well as all those unjustly arrested in the exercise of their freedom of expression," Anouar El Anouni, a spokesman for the bloc's diplomatic service, said.
Mohammadi, 53, who was last arrested in November 2021, has spent much of the past decade behind bars.
The 2023 Peace Prize laureate was granted temporary leave from prison on health grounds after problems related to her lungs and other issues in December 2024.
On Friday she was detained once again along with eight other activists at a ceremony for lawyer Khosrow Alikordi, who was found dead in his office last week, her foundation said.
Within Iran, the Mehr news agency cited the Mashhad governor Hassan Hosseini as saying individuals held at the ceremony had chanted "slogans deemed contrary to public norms" but did not name them.
"Mohammadi, who already had to endure years in prison because of her advocacy, bravely continues to use her voice to defend human dignity and the fundamental rights of Iranians, including freedom of expression, which must be respected at all times," El Anouni said.
Alikordi, 45, was a lawyer who had defended clients in sensitive cases, including people arrested in a crackdown on nationwide protests that erupted in 2022.
His body was found on December 5, with rights groups calling for an investigation into his death, which Norway-based NGO Iran Human Rights said "had very serious suspicion of a state murder".