The US government Thursday backed calls by the family of a Washington Post journalist held in Iran without charge that Iranian authorities should free him.
Jason Rezaian, a dual US-Iranian citizen who is the newspaper's Iran correspondent, was arrested at his home in Tehran on July 22, but the allegations against him have never been officially disclosed.
An open letter signed by his mother and brother, published on the Post's website, said: "If Iran has any evidence against Jason then why have we not heard of it?"
"If, after 100 days, Iran's professionally trained and liberally employed interrogators have found evidence against Jason then why has he not been charged and permitted to employ an attorney and defend himself?
"After 100 days, it's time for Iran to concede Jason's innocence and release him," it added.
Rezaian, 38, was arrested along with his wife Yeganeh Salehi, who is Iranian and also a reporter, and another couple, one of whom is a photojournalist and dual US-Iranian citizen.
Only Rezaian remains in custody. One conservative newspaper in Tehran accused him of espionage, and Iranian officials have hinted at that, saying his detention is a security matter.
"It has been a 100 days that Jason Rezaian... has been detained in Iran. That is a 100 days too long," State Department spokeswoman Jen Psaki told reporters on Thursday.
"We echo the appeals of his family and friends, and repeat our call for his immediate release, that he can be reunited with his loved ones."
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Rezaian's wife, who worked for Abu Dhabi-based English language newspaper The National, and the photojournalist remain on bail.
Despite pressure from the US State Department, Iran's President Hassan Rouhani, Foreign Minister Mohammad Javad Zarif and other officials have said the cases are a matter for the judiciary.
A top Iranian official defended the investigation, telling CNN television that charges could still be brought.
"Unfortunately, they have been involved in activities which our security people consider... definitely beyond journalism," said Mohammad Javad Larijani, head of the Iranian judiciary's human rights branch.
"Accusations, when it is considered as substantial and capable of being prosecuted by law, it becomes charges.
"So during the court process it will be definitely explained and determined whether they are serious charges or it could be dropped. They have ample opportunity to defend themselves," Larijani said.
However, the Post said it was "inexplicable and utterly unacceptable" that Rezaian has been held for 100 days.
"The time is long overdue for the Iranian authorities to release Jason and to allow him to be reunited with his family," said Douglas Jehl, the American newspaper's foreign editor.
Psaki also called for the release of other Americans held in Iran, including Amir Hekmati and Saeed Abedini.
And she again asked "the Iranian authorities for their cooperation in finding Robert Levinson" who disappeared seven years ago from Iran's Kish Island in the Gulf.