The husband of a British-Iranian woman imprisoned in Tehran has spoken of his hopes for her freedom as a senior Foreign Office minister visits the country.
Alistair Burt will hold talks with senior Iranian politicians and raise the cases of dual national detainees including Nazanin Zaghari-Ratcliffe and Kamal Foroughi.
Ms Zaghari-Ratcliffe's Iranian family have given Mr Burt a message warning that imprisonment is taking a physical and mental toll on the 38-year-old mother, who has a young daughter.
Her husband, Richard Ratcliffe, said he wanted Mr Burt to raise the issue of his wife's innocence as well as her incarceration, saying: "Having two passports should mean more protection for her rights, not less."
He added: "We hope he finds a way to encourage the Iranian authorities to allow Nazanin home reunited with her husband and daughter.
"In just over a week it will be 500 days of Nazanin being held.
"Gabriella was only 661 days old when her mother was originally taken - soon it will be half of her life growing up without her parents. Time passes, and it continues to take its toll."
Mr Burt's visit to Tehran will see him attend the official swearing-in ceremony for re-elected President Hassan Rouhani on Saturday.
The message to him from Ms Zaghari-Ratcliffe's family says the "unsuitable condition of the solitary confinement has deteriorated her health".
Ms Zaghari-Ratcliffe was arrested at Tehran Airport in April last year while visiting family in Iran with daughter Gabriella.
She was later jailed for five years for allegedly plotting to topple the Iranian government - a charge she has repeatedly denied.
She has been held alone at Evin prison for the past nine months and is suffering from mental health problems, as well as physical issues with her shoulder, neck, eyesight and teeth.
The family said they managed to get a psychiatrist in to see her, but added: "Being away from her daughter and husband has made her very fragile and desperate.
"The Iranian government keep promising her freedom, but it did not happen. She is near the end of her patience."
Mr Foroughi, 77, is held in the same jail for alleged espionage in Iran. He has strenuously maintained his innocence.
He was detained in 2011 before being convicted of espionage and possessing alcohol two years later
Roya Nobakht is another British-Iranian being held in Evin prison.
She was jailed for five years in 2013 for making anti-government comments on Facebook.
Amnesty International UK warned the Government that it must "significantly raise its game" over the detainees.
Director Kate Allen said: "Alistair Burt ought to use his time in the country to tell Iranian officials that the jailing of human rights activists and many others after grossly unfair trials on spurious national security charges is completely unacceptable and has got to stop."
Ahead of his trip Mr Burt said the UK was "keen to maintain dialogue" on issues including the detainees.
He said: "We hope to build further on improving UK-Iran relations during President Rouhani's second term.
"The president's personal commitment to the nuclear deal is welcome and it is vital both our countries work closely together to ensure the deal continues to be successfully implemented.
"We are also keen to maintain dialogue on Iran's regional policies, human rights and particularly our dual national detainees. Progress in all of these areas is important to the UK."