Iranian Nobel Peace Prize laureate Narges Mohammadi, one of the country’s most prominent human-rights advocates, was arrested at a public event Friday, her family said.

Mohammadi, 53 years old, was awarded the prize in 2023 for her three decades of fighting for democracy in Iran. She has spent years behind bars, and gained global attention for speaking out against the oppression of women and torture of dissidents under Iran’s theocratic government.

The activist’s brother Hamidreza Mohammadi told The Wall Street Journal that she was violently detained in the northeast Iranian city of Mashhad while attending a memorial service for Khosrow Alikordi, a lawyer who was recently discovered dead in his office. Her other brother, Mehdi Mohammadi, was with her at the event, he said.

Iran’s mission to the United Nations declined to comment.

Alikordi’s sudden death shocked Iran’s close-knit community of human-rights lawyers, many of whom expressed concern over what they called suspicious circumstances. His memorial drew a large crowd of supporters.

Mohammadi was giving a speech to attendees when security forces moved to disperse the crowd, her family said. They said her legs were beaten with a club, and she was pulled by her hair during the arrest.

“When Narges gives a speech, it is moving, and it affects a lot of people,” her brother Hamidreza said. “It could be that they just wanted to silence her at that moment.”

Her Paris-based Narges Foundation said several other high-profile human-rights activists were also detained at the event. The foundation didn’t state a reason for the detentions on Friday.

At the time of her arrest, Mohammadi was out of prison on a temporary medical reprieve granted late last year, following an invasive surgery. She had been serving multiple sentences for alleged propaganda activities, totaling more than 10 years’ imprisonment in Tehran’s notorious Evin Prison.

Write to Feliz Solomon at feliz.solomon@wsj.com