A British-Iranian academic has been arrested in Iran, the country has confirmed.
A spokesman for Iran's judiciary told state media that Abbas Edalat had been arrested on security charges.
Mr Edalat, a professor at London's Imperial College, was reportedly detained on 15 April while attending an academic workshop in Tehran.
The Foreign Office said it was "urgently looking into" the reports of his arrest.
On Thursday, an Iranian news agency reported that Mr Edalat was part of a "network" of British spies whose members have been identified and arrested.
According to state broadcaster IRIB, Iranian judiciary spokesman Gholamhossein Mohseni Ejehi told reporters in Tehran on Sunday: "I confirm his arrest on security charges, but I am unable to give details."
The Center for Human Rights in Iran (CHRI) said Mr Edalat was detained by the Iranian Revolutionary Guards. The group said guards had confiscated a computer, CDs and notebooks during the arrest.
Mr Edalat is a professor of computer science and mathematics. He had been a founder of an anti-war protest group that opposed sanctions in Iran.
Imperial College has said it is "concerned for his welfare" and "urgently seeking further information.
There are at least 30 dual nationals in jail in Iran - among them several dual British-Iranian nationals.
One of them - Nazanin Zaghari Ratcliffe, 39 - is currently serving a five-year jail sentence after being convicted of spying charges.
Mrs Zaghari-Ratcliffe, who was arrested at Tehran Airport on 3 April 2016, has denied the charges against her.