The Iranian Embassy in Ireland has warned that "there might be third-party adverse interests in publicising and politicising the case" of an Irish man who has been in jail in the country since October.
Bernard Phelan was arrested while working for a tourism company in Mashhad, Iran's second largest city, which is near the border with Afghanistan.
His family has said that Mr Phelan has gone on hunger strike, and expressed serious concern for his health.
In a statement today, the Iranian Embassy warned against efforts "trying to derail [the case] from its judicial processes".
"There might also be certain political interests in abusing this case in the context of misinformation against Iran with a view to smear the image of the country", it said.
Caroline Massé Phelan, Brendan's sister, said that her brother "just can't stand it anymore", and has also surrendered medication he needs for a heart problem, and a condition which affects his bones.
"The situation is just so bad for him in the prison, he just doesn't see any sign of getting out of there," she said.
Bernard Phelan was arrested for allegedly taking photographs of police officers and a mosque which had been burned.
He denies all charges against him.
Members of Mr Phelan's family were briefed today by Department of Foreign Affairs officials, who said the case has been raised directly with the Iranian authorities.
The Iranian Embassy said that it has reassured Mr Phelan's father "that no effort has been spared to facilitate his son’s release on humanitarian grounds".
It also said that Mr Phelan "receives his medicine as prescribed and is treated fairly well in a prison with standard conditions and medical services".
Ms Massé Phelan said her brother is sharing a prison cell with up to 16 other people in very basic conditions.
Speaking to RTÉ's News at One, she said no official charges have been brought against him yet, although he has faced various accusations.
"The prison judiciary has said that propaganda against the regime is his charge, for taking photographs," she said.
"He’s had charges nearly once a month. The first was taking photographs, then it was sending photographs to the press, then it was taking two small pieces of pottery from a village he had visited, which they say were 900 years old."
"He denies all charges, but he hasn’t been brought to court or judged and he hasn’t had access to a lawyer," she said.
Ms Massé Phelan said her brother has both French and Irish nationality and the Irish and French consulates are working together to try to secure his release.
"He loves Iran, he’s done everything to promote Iran. It just doesn’t make sense for him to be held and he just wants out."
Ms Massé Phelan said her 97-year-old father has written to TDs, ambassadors and President Michael D Higgins.
She urged the Government to maintain constant pressure on Iran and continue negotiations with Iranian authorities "as much as possible".
The Iranian Embassy noted that Bernard Phelan is a dual national of France and Ireland.
"Since his effective nationality is French, and he had arrived in Iran with a French passport, his case has been handled by the French Embassy in Iran", it said.
"He has also been given the opportunity of having regular phone contacts with the Irish Charge d'Affairs in Tehran. Relevant authorities in the Iranian Ministry of Foreign Affairs and the Judiciary have been dealing with the case with particular attention."
