Theresa May has pressed Iranian president Hassan Rouhani over a London woman jailed for allegedly plotting to topple the Tehran government.
Charity worker Nazanin Zaghari-Ratcliffe was jailed for five years earlier this month but the UK authorities have not been given details of the sentence or the charges.
The Prime Minister used her first meeting with President Rouhani to push for progress on the case.
Mrs Zaghari-Ratcliffe, from Hampstead, north-west London, was arrested at Imam Khomeini airport on April 3 as she was trying to return to Britain after a holiday visiting family with her daughter Gabriella.
Mrs May met the Iranian leader in the margins of the United Nations General Assembly in New York.
Mrs May is understood to have raised concerns about the charges and the sentencing.