Jason Rezaian, the Washington Post correspondent who was unjustly imprisoned by Iran for 18 months, and his family have filed a lawsuit against the Iranian government. (The Washington Post)

Washington Post reporter Jason Rezaian and his family filed a federal lawsuit Monday against the Iranian government, claiming he was taken hostage and psychologically tortured during his 18 months in prison in an effort by Tehran to influence negotiations for a nuclear agreement with Iran.

The suit, filed in U.S. District Court in the District of Columbia, says Rezaian was targeted for arrest to gain advantage in a prisoner exchange and to “extort” concessions from the U.S. government in the multinational talks over lifting sanctions if Iran agreed to limits on its nuclear program.

Iranian officials repeatedly told Rezaian and his wife, Yeganeh Salehi, who also was detained for more than two months, that Rezaian had “value” as a bargaining chip for a prisoner swap, the suit says. The filing also links key moments in the nuclear negotiations to Rezaian’s treatment in the judicial system, from arrest to conviction to sentencing, and ultimately his release on the day the deal was implemented.

“For nearly eighteen months, Iran held and terrorized Jason for the purpose of gaining negotiating leverage and ultimately exchanging him with the United States for something of value to Iran,” the suit states.

Rezaian; his brother, Ali Rezaian; and their mother, Mary Rezaian, are asking for an unspecified sum for damages under the “terrorism exception” to the Foreign Sovereign Immunities Act. That law generally bars U.S. citizens from suing foreign governments in domestic courts, but exceptions are made for terrorist acts, torture or hostage-taking by countries, including Iran, that the State Department has designated as state sponsors of terrorism. The suit accuses Iran of all three.

Rezaian and Salehi, who was born in Iran and married Rezaian there, were arrested on July 22, 2014, by Iranian agents wearing surgical masks who forced their way into the couple’s apartment and took them for questioning at Evin prison, a notorious site for political prisoners. Salehi was freed 71 days later on a $32,000 bail provided by her brother-in-law, Ali.

Rezaian was eventually tried and convicted on espionage and related charges, according to Iranian state media accounts. But the Iranian government has never officially disclosed the specifics of his conviction in a closed-door trial or the sentence imposed by a judge known for meting out harsh punishments.

The lawsuit provides details of Rezaian’s incarceration that had never before been publicly revealed.

Both Rezaian and Salehi were repeatedly subjected to psychological and physical abuse during lengthy interrogations, the suit says. Their captors at turns threatened to dismember or execute them. Interrogated in isolation and often deprived of sleep, each also was warned that the other might be maimed or executed, and that the same fate could befall other family members in Iran, according to the filing.

Jason Rezaian, second from left, stands in front of journalists with, from left, mother Mary Rezaian, wife Yeganeh Salehi and brother Ali Rezaian at the U.S. military medical center at Landstuhl, Germany, where Jason and two other Americans released from an Iranian prison were examined in January. (Jabin Botsford/The Washington Post)

The ordeal was so intense that Rezaian, Salehi and Rezaian’s brother, Ali, all contemplated suicide, the suit says. Now — almost nine months after Rezaian and four other U.S. citizens were released on the day the nuclear deal was implemented — Salehi, the Rezaian brothers and their mother are still afflicted with trauma and guilt, according to the suit.

“For 544 days, Jason suffered such physical mistreatment and severe psychological abuse in Evin Prison that he will never be the same,” the suit states. “He will require specialized medical and other treatment for the rest of his life.”

Salehi is not a plaintiff in the suit. Nor is The Washington Post. Rezaian is on leave from The Post for a year as a Nieman fellow at Harvard University.

“Iran’s unconscionable actions have inflicted deep and lasting wounds on The Washington Post’s Jason Rezaian and his family,” said Executive Editor Martin Baron, who during the reporter’s imprisonment often criticized what he called Iran’s “system of injustice.”

“This legal filing is a stark telling of Iran’s brutal and heartless treatment of an innocent journalist and his wife, and the impact on those who love him. While this legal action is being taken solely by Jason and his family, The Post continues to support the Rezaians through their long and painful recovery.’’

The Rezaian lawsuit is the latest attempt by Americans to have the U.S. justice system provide compensation for harms inflicted by the Iranian government — in particular, by the powerful and hard-line Revolutionary Guard Corps, which fiercely opposed the nuclear deal and has tried to thwart many initiatives of President Hassan Rouhani, a relative pragmatist. The corps is named as a co-defendant in the suit.

“This was really one of the few ways they felt they could try to hold Iran publicly accountable,” said David Bowker, Rezaian’s attorney. “Ideally, it will deter this kind of behavior toward other innocent people.”

Rezaian and his family declined to discuss the case, referring questions to their lawyer. The Iranian mission to the United Nations did not reply to an email requesting comment.

In a number of suits brought against it over the years, Iran has not responded, resulting in default judgments.

Congress and U.S. courts have provided a legal framework for Americans to sue Iran and be compensated. The State Department has labeled Iran the top state sponsor of terrorism in the world. Sudan and Syria are also on the list.

In April, the Supreme Court upheld a law allowing American victims of terrorism and their families to collect almost $2 billion in seized Iranian assets. The case involved relatives of people killed or injured in the 1983 bombing of the U.S. Marine Corps barracks in Beirut. Iran labeled the decision “confiscation” and “theft.”

The closest precedent to Rezaian’s case involves Nik Moradi, an Iranian American who was seized during a family visit in 2007 and accused of spying for the United States. More than six months before his release on bail, he said, he was subjected to physical and mental torture during interrogations. In 2013, Moradi and his wife sued Iran in U.S. federal court under the Foreign Sovereign Immunities Act. The couple was awarded $20 million in a default judgment after Iran failed to respond.

One possible venue for securing payment on a judgment is the Victims of State Sponsored Terrorism Fund, created last year by Congress to compensate the Americans held hostage in Iran during the takeover of the U.S. Embassy in Tehran after the 1979 revolution. It also set aside money for victims with court judgments against state sponsors of terrorism, funded by money from a civil penalty paid by BNP Paribas bank for violating sanctions against Iran, Cuba and Sudan.

The lawsuit provides dark glimpses of Rezaian’s 50 days in solitary confinement in a small, dank, cockroach-infested cell. Anxiety and depression made him hallucinate, as he perceived the walls moving and talking. The cell was constantly lighted, and a noisy fan hindered his sleep. Rezaian slept on the floor, and prison officials eventually gave him tranquilizers to induce sleep. His food sometimes had concrete, rocks, dirt and other inedible objects mixed in.

“During his time in solitary confinement, Jason believed he was losing his mind,” the suit says.

In the initial months of his imprisonment, Rezaian was taken blindfolded several times a day to an underground room for interrogations that lasted hours. He was forced to write down his answers, which prison officials translated into Farsi before trying to coerce him to sign without explaining the translations.

In an effort to get Rezaian to confess to espionage, the suit says, one interrogator threatened him with beheading. Another held out the carrot of a video confession as his only chance for freedom.

“They threatened Jason with physical mutilation, such as cutting off his limbs, and repeatedly told Jason that he would never see Yeganeh alive again,” the suit says.

Though Salehi is not a plaintiff, her agony is clear in the suit’s dry legalese.

During her detention, Salehi was blindfolded as interrogators hit the table, broke glass and kicked her chair, startling her. One interrogator threatened to cut off her left leg and right hand or arm. They told her they would throw her husband off a cliff if she did not incriminate him.

By the time she was released, her legs would go numb and she sometimes fainted when sitting down. She had to shear off her hair because it was so matted. She had skin lesions. On her infrequent visits to the prison to see her husband, she sometimes was made to don a prison uniform and told she might be detained again, the suit says. Convinced that her husband would die in Evin prison, she considered killing herself to draw attention to his plight.

Ali Rezaian, who quit his job to work full time campaigning for his brother’s release, also grew despondent, according to the suit. Iranian agents tailed him when he went to Geneva to appeal for help from the U.N. Human Rights Council, and his mother was held against her will in Iran.

“He contemplated suicide in the fall of 2015, having lost faith that his brother would ever be released,” the suit states. “At the time, Ali believed that only by ending his own life could he prompt action by defendants or others, to free Jason.”

Jason Rezaian now experiences depression, sleeplessness, short-term memory loss and other symptoms associated with post-traumatic stress disorder, the suit says. He grows anxious in large crowds, fears for his family’s safety and has grown more “detached” from them. He sees a psychologist.

“Plaintiffs live in constant fear that Iranian agents are spying on them, plotting additional acts of terrorism and planning ways to hurt them and their family members again,” the suit says.

Ann E. Marimow contributed to this report.