Award-winning Iranian human rights lawyer Nasrin Sotoudeh was arrested on Wednesday on unknown charges, her husband said, weeks after she was barred from practising for three years.
The couple's car was surrounded by intelligence agents on a highway in Tehran, Reza Khandan wrote on his Facebook page.
"Nasrin and I were arrested. I was freed but Nasrin is still in detention," he said, describing it as "their gift for World Human Rights Day" which was being marked on Wednesday.
Sotoudeh, who won the European parliament's prestigious Sakharov rights prize in 2012, was released from jail last year halfway through a six-year sentence for "actions against national security" and spreading "propaganda against the regime".
In September a Tehran court barred her from practising for three years.
Khandan gave no indication of why Sotoudeh was arrested but a message she posted on her husband's Facebook account over the weekend was critical of restrictions on education in Iran, as well as a lack of employment opportunities for political opponents.
Hailing from a religious middle-class family, Sotoudeh was among the few Iranian lawyers to take high-profile rights and political cases, including juveniles facing the death penalty, before her arrest in 2010.
She has defended journalists and activists including Nobel Peace laureate Shirin Ebadi. When in jail she staged two hunger strikes, in protest at the conditions at Evin Prison in Tehran and at a ban against seeing her son and daughter.
Sotoudeh was released in September 2013 shortly before Iran's then newly elected President Hassan Rouhani, who had campaigned on a pledge to improve civil rights, attended the UN General Assembly.
In New York at this year's opening of the Assembly, the reform-minded leader denied that human rights were worsening in Iran.