A British-Iranian dual citizen has been detained by Iranian authorities since mid-April, a human rights group and friends of the man's family say.
The New York-based Center for Human Rights in Iran (CHRI) on April 25 identified the man as Abbas Edalat, a professor of computer science and mathematics at Imperial College in London.
"Iran's continued arbitrary arrests of dual nationals without transparency and lack of due process is extremely concerning," said Hadi Ghaemi, CHRI's executive director.
Edalat traveled to Iran from his home in London at an unknown date to attend an academic workshop, according to family friends and the rights group.
He was arrested at his family's home in Tehran on April 15 by Iran's hard-line Islamic Revolutionary Guards Corps (IRGC) and taken to the notorious Evin prison. Security forces seized a computer, phone, textbooks, and other items.
Friends say the charges are unknown and the man has not had access to a lawyer.
The CHRI said Edalat refused to post bail on April 25, arguing that he was innocent and should be released immediately.
The British Foreign Office said in a statement that it was "urgently seeking information from the Iranian authorities following reports of the arrest of a British-Iranian dual national."
In early 2017, Edalat said in an interview that he had stopped submitting research papers to U.S. conferences after President Donald Trump issued a travel ban on mostly Muslim-majority countries, including Iran.
The CHRI described him as the founder of the U.S.-based Campaign Against Sanctions and Military Intervention in Iran, a group that opposes foreign intervention in Iran.
Iran's IRGC has arrested at least 30 dual nationals since 2015, mostly on spying charges, according to Reuters.
At least two other British-Iranian citizens are known to be held in Iran.
One unidentified British-Iranian man was sentenced in March to six years in prison on spying charges.