Secretary of State John Kerry called for the release of Pastor Saeed Abedini on Friday, along with other Americans being held prisoner in Iran.

In a press statement, Kerry described the circumstances of the men's capture, and urged Iranian officials to send them home.

"On September 26, Mr. Abedini will have been detained for two years in Iran, on charges related to his religious beliefs," Kerry said. "Mrs. Abedini has spoken eloquently about the difficulties her family has faced during this challenging time."

Pastor Abedini, who became a Christian in 2000, maintains that he travelled to his native country to help build a state-run orphanage. He has reportedly been beaten by inmates and guards while incarcerated, and was temporarily transferred to a hospital after suffering internal injuries from the assaults. He was sentenced to eight years in prison in January 2013.

Abedini's wife, Nagmeh, reported last month that her husband has received death threats from members of the Islamic State who are imprisoned with him. His notoriety as a Muslim-to-Christian convert and an American make him a target, and the American Center for Law and Justice revealed that terrorist organisation Al-Qaeda has also threatened Abedini's life. The pastor has had to hide in his cell to avoid being attacked, Nagmeh said.

Secretary Kerry also called for the release of Amir Hekmati and Jason Rezaian, and for the Iranian government to "work cooperatively" with the U.S. government to find Robert Levinson.

The date of the press statement, Aug. 29, marked the three-year anniversary of Hekmati's capture on false espionage charges. He was sentenced to death, but the Iranian Supreme Court overturned the ruling. Hekmati remains imprisoned, awaiting a retrial.

"Mr. Rezaian, a reporter for the Washington Post, is being detained in an unknown location," Kerry said. "His love of Iran is seen in his reporting – portraits of the generosity and kindness of the Iranian people."

Rezaian, his wife, Yeganeh Salehi, and two photojournalists were arrested on July 22 over "security issues". One of the photojournalists was later released. No further information on the nature of the charges against them has been released publicly.

A 20-year FBI veteran, Levinson was reportedly on a CIA mission when he was kidnapped on March 9, 2007 by Iranian authorities. Both the US government and Levinson's family denied for years that he was on a CIA mission, stating instead that he was working as a private investigator. In December, the family admitted the truth, and provided proof of the government relationship. Iran has not admitted that they are holding Levinson.

"The United States remains committed to returning all of them to their families, friends, and loved ones," Kerry's statement read.

"We ask the Government of the Islamic Republic of Iran to immediately release Amir Hekmati, Saeed Abedini, and Jason Rezaian and respectfully request the Government of the Islamic Republic of Iran work cooperatively with us to find Mr. Levinson and bring him home."