Iran revealed on Sunday that it had sentenced an unidentified Iranian-British dual citizen to six years in jail for spying for Britain in a case that appears not to have previously been disclosed.

No details of the case were given, including when the person was arrested or where.

The judiciary’s Mizan news agency said Tehran prosecutor Abbas Jafari-Dolatabadi had “referred to a six-year prison sentence for an agent of England’s intelligence service”. It quoted him as saying the same British-Iranian citizen was also under investigation in a separate case related to a private bank, giving no further details.

Iran does not recognise dual citizenship, which limits the access foreign embassies have to their dual citizens held there.

A spokeswoman for Britain’s Foreign Office was not immediately able to comment.

At least two British-Iranian citizens are known to be held in Iran, including Nazanin Zaghari-Ratcliffe, a project manager with the Thomson Reuters Foundation, the charitable arm of the parent company of Reuters, whose case was taken up by the foreign secretary, Boris Johnson, during a visit to Iran in December.

She has been sentenced to five years for plotting the overthrow of Iran’s government. Her employers and the British government said she was in Iran visiting relatives when she was arrested in April 2016.

Kamal Foroughi, a 78-year-old British-Iranian businessman, was arrested in 2011 and convicted of espionage and alcohol possession charges.

The Foreign Office said it has raised both cases with the Iranian authorities. The families of both those held deny the charges.

Iran’s Revolutionary Guards have arrested at least 30 dual nationals since 2015, mostly on spying charges, Reuters reported in November.