Jason Rezaian, the Tehran correspondent for The Washington Post, and his wife Yeganeh Salehi, an Iranian journalist, are shown in Tehran in September 2013. (Stringer/EPA)

The family of a Washington Post reporter held without charge in Iran for more than three months called Wednesday on the authorities in Tehran to free him.

An open letter signed by Jason Rezaian’s brother, Ali, and his mother, Mary Breme Rezaian, was released 100 days after Rezaian was arrested under still-vague circumstances, along with his wife and another couple. Rezaian’s family said he is being held in solitary confinement in the notorious Evin prison, which houses common criminals as well as dissidents, intellectuals and journalists.

Because no charges have been brought against him, Rezaian has been prohibited from hiring a lawyer, his family said.

“If Iran has any evidence against Jason then why have we not heard of it?” the family statement said. “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.”

Mary Rezaian pleads for the Iranian government to release her son, Washington Post correspondent Jason Rezaian, and his wife Yeganeh Salehi. The two were arrested on July 22 on undetermined charges in Tehran along with another couple. Rezaian remains in custody, while Salehi and the couple have all been released. (Provided to The Washington Post)

Rezaian, 38, is The Post’s correspondent in Tehran. He holds dual U.S. and Iranian citizenship. The State Department has called for his release and asked about his condition through the intermediary country of Switzerland; the United States and Iran do not have diplomatic relations. But Iran does not recognize dual nationality and dismisses any U.S. right to have a say in the case.

Rezaian and his wife, an Iranian journalist, were arrested together with another couple on July 22. All but Rezaian, who requires daily medication to treat his high blood pressure, have been released. Rezaian’s wife, Yeganeh Salehi, was freed on bail this month.

“It is inexplicable and utterly unacceptable that Jason Rezaian, the Post’s Tehran correspondent, remains in Iranian custody,” said Douglas Jehl, The Post’s foreign editor. “After 100 days, the time is long overdue for the Iranian authorities to release Jason and to allow him to be reunited with his family.”

Iran has never publicly stated the grounds for the arrests or

what specific accusations Rezaian faces.

“Unfortunately, they have been involved in activities which our security people consider . . . activities definitely beyond journalism,” Mohammed Javad Larijani, head of the judiciary’s human rights council, said in a CNN interview Wednesday.

“Accusations — when it is considered as substantial and capable of being prosecuted by law, it becomes charges,” he added. “So it was not pure accusations.”

Larijani said that charges will be explained during the court process and that Rezaian and others will “have ample opportunity to defend themselves.”

Larijani, the son of an important ayatollah, has frequently defended Iran to Western audiences, including on the subject of the country’s growing number of executions for drug crimes.

Since Salehi was released three weeks ago, she has visited Rezaian several times, according to his brother. He has not seen a doctor during his confinement despite family requests that he have access to a physician to ensure he has no long-term ailments, Ali Rezaian said.

The lengthy detention, he added, makes him “hopeful that leaders higher up in Iran will see the absurdity of holding Jason for this long, given that there has never been any public mention of any evidence against him.”