Image copyright 'Free Nazanin' campaign Image caption Nazanin Zaghari-Ratcliffe and her daughter Gabriella are still in Iran

Iran has accused a British-Iranian charity worker arrested after visiting family with her two-year-old daughter of seeking to "overthrow the regime".

Nazanin Zaghari-Ratcliffe, 37 of north London was held in April, while she was at an airport with daughter Gabriella.

The state IRNA news agency reports that a provincial military unit affiliated to Iran's Revolutionary Guard said she had "participated in coup plots".

The Foreign Office said it was urgently seeking information on her situation.

According to IRNA, the Sarallah Corps, which arrested Mrs Zaghari-Ratcliffe, said in a statement: "Through membership in foreign companies and institutions, she has participated in designing and executing media and cyber plots with the aim of the peaceful overthrow of the Islamic Republic establishment."

Solitary confinement

Mrs Zaghari-Ratcliffe, who travelled to Iran on an Iranian passport, was arrested at Tehran's Imam Khomeini Airport on 3 April and taken to Kerman in the south-east of the country.

Her daughter had her British passport taken away and is staying with Mrs Zaghari-Ratcliffe's parents.

Mrs Zaghari-Ratcliffe was jailed in Kerman, where she was kept in solitary confinement for several weeks, before being transferred to a prison in Tehran.

She works for the London-based Thomson Reuters Foundation charity.

Image caption Richard Ratcliffe has been campaigning for the return of his wife and baby

Her husband Richard Ratcliffe, who has been trying to get a visa to visit her, has been campaigning for her return to the UK.

Last month, Mr Ratcliffe said it was "hard to understand how a young mother and her small child on holiday could be considered an issue of national security".

A Foreign Office spokeswoman said: "We are urgently seeking information from the Iranian authorities on the reported accusations being made against Mrs Zaghari-Ratcliffe.

"We have raised this case repeatedly and at the highest levels and will continue to do so at every available opportunity. We have also been supporting Mrs Zaghari-Ratcliffe's family since we were first made aware of her arrest.

"Minister for the Middle East, Tobias Ellwood, has met personally with the family to reassure them that we will continue to do all we can on this case."