An Iranian employee of the British Council who was arrested in Tehran and sentenced to 10 years in prison over internationally criticised espionage charges has been freed and has returned to the UK, the organisation said.

Iranian authorities did not immediately acknowledge the release of Aras Amiri, but it came amid negotiations in Vienna between Tehran and world powers, including the UK, over its tattered 2015 nuclear deal.

The British Council said on Wednesday that an appeal her lawyers made to Iran’s Supreme Court had been successful. Ms Amiri worked for the council’s London office.

“We have always refuted the original charges made against Aras,” the council said in a statement.

“We are very proud of her work in our London office as an arts programme officer supporting a greater understanding and appreciation of Iranian culture in the UK.”

In Tehran, her lawyer, Hojjat Kermani, confirmed in an interview with the Associated Press that Ms Amiri had been released.

He said Iran’s Supreme Court had determined that her earlier espionage conviction in the country’s Revolutionary Court was “against Shariah”, or Islamic law.

Mr Kermani said Ms Amiri left Tehran on Monday but had been free from prison in recent months as she appealed against a travel ban.

Iran announced her conviction in 2019. Authorities had accused her of spying on cultural activities in Iran.

The British Council previously said she had travelled to Tehran to visit family on a private trip that did not involve her work at the non-political organisation which works in arts, culture and education.

As tensions with the West simmer, Iranian authorities have arrested a number of British dual-nationals in recent years. Rights groups accuse Tehran of holding them as bargaining chips for money or influence in negotiations with the West, something Tehran denies.

A British-Iranian worker for the Thomson Reuters Foundation, Nazanin Zaghari-Ratcliffe, has been detained for more than five years in Tehran. After completing her sentence last year, she was released from prison — only for authorities to present new charges of “spreading propaganda against the regime” which she denies.

Anoush Ashoori, another dual national, was sentenced to 12 years at the same time as Ms Amiri and remains in detention.

A UN panel has criticised what it describes as “an emerging pattern involving the arbitrary deprivation of liberty of dual nationals” in Iran.

Ms Amiri’s release comes as world powers negotiate over Tehran’s collapsed nuclear deal in Vienna. The negotiations have dragged on for weeks with little sign of progress under recently elected hardline President Ebrahim Raisi.

Iranian and Gulf Arab diplomats flew this week for talks in China, another signatory to the nuclear deal.

European delegates have warned that time is running out to save the deal as Iran accelerates its nuclear programme, spinning uranium in advanced centrifuges up to 60% purity — a short step from weapons grade levels.