Iran has released the journalist Yeganeh Salehi who was arrested almost three months ago alongside her husband, the Washington Post's Tehran correspondent Jason Rezaian, an official said Monday.

Rezaian, who holds dual US-Iranian citizenship, remains in custody but Salehi, an Iranian, was freed on bail in the middle of last week, the official said, confirming an earlier report by the Post.

The couple's detention has attracted considerable attention given the ongoing talks between Iran and the United States and other world powers over the Islamic republic's disputed nuclear programme.

An Iranian official said in August that the case was a security matter, but did not specify what the journalists were accused of.

"She has been freed," Mohammad Koushesh, director general of the Foreign Media Department at Iran's Ministry of Culture told AFP, referring to Salehi. "We hope that Jason is released soon."

The ministry has "done everything possible" to secure Salehi and Rezaian's release, Koushesh said.

"It is not something that is in our hands," he added, alluding to the case being a matter for the judiciary, which is independent of President Hassan Rouhani's government.

According to Reporters Without Borders, a Paris-based press freedom group, more than 50 journalists and bloggers are in Iranian custody.

However, Salehi's press card remains valid and "no decision has been taken" that would stop her working as a reporter, Koushesh said, contrary to the Post's report, which said her credentials had been withdrawn.

Salehi was able to visit her husband over the weekend and told his brother that they were both "physically healthy" despite spending more than two months behind bars, according to the Post.

Rezaian's high blood pressure and daily medication needs have raised concerns about his health.

Salehi has refused to discuss her detention.

However her family said in a statement: "We are thankful Yeganeh has been released on bail. We remain confident that Jason has committed no crime. We pray that the Iranian government will conclude that Jason should be released as well."

It remains unclear why Rezaian, 38, and Salehi were arrested on July 22 or what charges they are facing. One conservative newspaper in Tehran has accused Rezaian of espionage.

Last month, Foreign Minister Mohammad Javad Zarif said Rezaian was being questioned "for what he has done as an Iranian citizen".

Iran does not recognise dual citizenship and has therefore rejected State Department requests about Rezaian and those arrested with him.

Tehran and Washington have had no formal diplomatic ties since the US hostage crisis that broke out in the Iranian capital in 1980, following the Islamic revolution the previous year.

"It is long past time for the Iranian authorities to release Jason and to permit him and Yegi to leave the country," said Post foreign editor Douglas Jehl in the American newspaper's report Sunday.

Another woman, a dual Iranian-US national who works as a photojournalist, was arrested with her husband at the same time as Salehi and Rezaian, but both were later released.